I have spent a lot of time trying to norrow this down but did find an interesting fact... The Total time does not need to be incorporated at all.. I have a lot of working ringtones and a lot not working. I can not figure out what the deal is... I came up with my GUID by using a WEP Key Generator at 152bit... This would generate a random HEX number that I used to punch in for the GUID because I noticed that the iphoneringtonemaker program was doing the same concept.. It took me forever to get Grind.mp3/m4r working I renamed it to Grin.mp3/m4r and it still didn't work, then I changed it to grin.mp3/m4r and it worked just fine. I have no clue what is the deal but can definitely confirm you do not need Total Time or any other fields to make them work.
I have a few more ideas but my time has run out tonight

Damnit thought I would have this one figured out.
my Ringtones.plist:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Ringtones</key>
<dict>
<key>cran.mp3</key>
<dict>
<key>GUID</key><string>542c7137646d61206c3b413a563d2734</string>
<key>Name</key><string>Crank</string>
</dict>
<key>cran.m4r</key>
<dict>
<key>GUID</key><string>542c7137646d61206c3b413a563d2734</string>
<key>Name</key><string>Crank</string>
</dict>
<key>grin.mp3</key>
<dict>
<key>GUID</key><string>2e696b61222865346f50297b6c687772</string>
<key>Name</key><string>Grind</string>
</dict>
<key>grin.m4r</key>
<dict>
<key>GUID</key><string>2e696b61222865346f50297b6c687772</string>
<key>Name</key><string>Grind</string>
</dict>
<key>40oz.m4a</key>
<dict>
<key>GUID</key><string>242f61517a5a4e5d41574b353c414236</string>
<key>Name</key><string>40oz</string>
</dict>
<key>40oz.m4r</key>
<dict>
<key>GUID</key><string>242f61517a5a4e5d41574b353c414236</string>
<key>Name</key><string>40oz</string>
</dict>
<key>badf.m4a</key>
<dict>
<key>GUID</key><string>7270796d334d645645464e296b20423d</string>
<key>Name</key><string>badf</string>
</dict>
<key>badf.m4r</key>
<dict>
<key>GUID</key><string>7270796d334d645645464e296b20423d</string>
<key>Name</key><string>badf</string>
</dict>
<key>ball.m4a</key>
<dict>
<key>GUID</key><string>593e28692053727472712a383231624b</string>
<key>Name</key><string>ball</string>
</dict>
<key>ball.m4r</key>
<dict>
<key>GUID</key><string>593e28692053727472712a383231624b</string>
<key>Name</key><string>ball</string>
</dict>
<key>ffff.m4a</key>
<dict>
<key>GUID</key><string>76272b6e4f736f42582f2a443e652966</string>
<key>Name</key><string>AAAA</string>
</dict>
<key>ffff.m4r</key>
<dict>
<key>GUID</key><string>76272b6e4f736f42582f2a443e652966</string>
<key>Name</key><string>AAAA</string>
</dict>
<key>djsr.m4a</key>
<dict>
<key>GUID</key><string>487375635b2f2d594165506727643d2b</string>
<key>Name</key><string>djsr</string>
</dict>
<key>djsr.m4r</key>
<dict>
<key>GUID</key><string>487375635b2f2d594165506727643d2b</string>
<key>Name</key><string>djsr</string>
</dict>
<key>dont.m4a</key>
<dict>
<key>GUID</key><string>4e54327632316b5f6746665b6b707565</string>
<key>Name</key><string>dont</string>
</dict>
<key>dont.m4r</key>
<dict>
<key>GUID</key><string>4e54327632316b5f6746665b6b707565</string>
<key>Name</key><string>dont</string>
</dict>
<key>geto.m4a</key>
<dict>
<key>GUID</key><string>274a4d24573646307366384f673e4f36</string>
<key>Name</key><string>geto</string>
</dict>
<key>geto.m4r</key>
<dict>
<key>GUID</key><string>274a4d24573646307366384f673e4f36</string>
<key>Name</key><string>geto</string>
</dict>
<key>krso.m4a</key>
<dict>
<key>GUID</key><string>36463f537450277e77637331363c7342</string>
<key>Name</key><string>krso</string>
</dict>
<key>krso.m4r</key>
<dict>
<key>GUID</key><string>36463f537450277e77637331363c7342</string>
<key>Name</key><string>krso</string>
</dict>
<key>news.m4a</key>
<dict>
<key>GUID</key><string>4921754531595f275a755a275f384c34</string>
<key>Name</key><string>news</string>
</dict>
<key>news.m4r</key>
<dict>
<key>GUID</key><string>4921754531595f275a755a275f384c34</string>
<key>Name</key><string>news</string>
</dict>
<key>root.m4a</key>
<dict>
<key>GUID</key><string>5e6666275675523d505c36772051567e</string>
<key>Name</key><string>root</string>
</dict>
<key>root.m4r</key>
<dict>
<key>GUID</key><string>5e6666275675523d505c36772051567e</string>
<key>Name</key><string>root</string>
</dict>
<key>sant.m4a</key>
<dict>
<key>GUID</key><string>223e3f39273a412f395d7c4e6a3c6d69</string>
<key>Name</key><string>sant</string>
</dict>
<key>sant.m4r</key>
<dict>
<key>GUID</key><string>223e3f39273a412f395d7c4e6a3c6d69</string>
<key>Name</key><string>sant</string>
</dict>
<key>scar.m4a</key>
<dict>
<key>GUID</key><string>7463215c705f385f505669696869326f</string>
<key>Name</key><string>scar</string>
</dict>
<key>scar.m4r</key>
<dict>
<key>GUID</key><string>7463215c705f385f505669696869326f</string>
<key>Name</key><string>scar</string>
</dict>
<key>smok.m4a</key>
<dict>
<key>GUID</key><string>4f40644f41687d3f567756295e614230</string>
<key>Name</key><string>smok</string>
</dict>
<key>smok.m4r</key>
<dict>
<key>GUID</key><string>4f40644f41687d3f567756295e614230</string>
<key>Name</key><string>smok</string>
</dict>
<key>were.m4a</key>
<dict>
<key>GUID</key><string>25717959715e47747272376956245c51</string>
<key>Name</key><string>were</string>
</dict>
<key>were.m4r</key>
<dict>
<key>GUID</key><string>25717959715e47747272376956245c51</string>
<key>Name</key><string>were</string>
</dict>
<key>what.m4a</key>
<dict>
<key>GUID</key><string>492f61646f5e2b4230554d624c382956</string>
<key>Name</key><string>what</string>
</dict>
<key>what.m4r</key>
<dict>
<key>GUID</key><string>492f61646f5e2b4230554d624c382956</string>
<key>Name</key><string>what</string>
</dict>
<key>wron.m4a</key>
<dict>
<key>GUID</key><string>33255341637a38514b3940424143535f</string>
<key>Name</key><string>wron</string>
</dict>
<key>wron.m4r</key>
<dict>
<key>GUID</key><string>33255341637a38514b3940424143535f</string>
<key>Name</key><string>wron</string>
</dict>
</dict>
</dict>
</plist>