When you want to add an alarm in iOS, what you normally do is go to your Clock application and tap on the "+" button in the alarm interface. From here, you can choose a time when you want your alarm to go off.
The major downfall to this is that you have to do the math yourself. If you know you want an alarm to go off in another 30 minutes, you have to add 30 minutes to the existing time to know what time you want the alarm to go off. If you're usign a more complex number than 30 minutes, then it won't be so easy.
A new free jailbreak tweak called TimerAlarms
by iOS developer L4grange is now available that takes all of the guesswork out of your responsibility. The tweak allows you to create alarms from the timer interface in the Clock application. A new "+" button is added to the timer interface, as shown above, that leads you to the alarm interface.
You will also notice that we have the timer set at 30 minutes, so when we go to create a new alarm based off of the timer, the alarm automatically sets itself for 30 minutes past the current time. This works for any timeframe that you put in the timer interface, so if you put 47 minutes, the alarm would auto-fill to 47 minutes past the current time, or if you put 1 hour and 28 minutes, the alarm would auto-fill to 1 hour and 28 minutes past the current time.
It can come in handy if you want a quick alarm without have to do the math yourself, and honestly makes the interface a lot easier to use. If you would like to give TimerAlarms a try, it's available for free right now in Cydia's BigBoss repository. There are no options to configure. The tweak is also open source, which means the source code is available on GitHub at this link
iPhone 5 running iOS 7.1.2
You can watch our video review of TimerAlarms at this link: