Native Andriod app?
The itunes store has many time tracking apps but the android market has none AFAIK. SlimTimer is one of the best timers I have found and I have looked at many. You could be a serious contender if you were the first on the Android market.
Xpert-Timer for android is okay, but one can not share info on working time with colleagues neither sync tracking info taken off-line.
or write a trello add-in which lets you use (actually can we say leverage here?!) The existing mobile trello client
mtimer doesn't work very well at all. it doesn't sync to my current task list and doesn't upload my logged time to my account.
I use mtimer
did you try "mtimer" for android?