Hi there, there are probably thousands of time sheet apps but one I have used is called Hours Keeper:Time Tracker.
It's pretty simple and easy to use, will handle multiple jobs, and notes, even invoicing if you want. From memory it was free but that may have changed, it was a while ago.
Any way, hope this helps, picture of the app to download is below. Just search Hours keeper on App Store.
Andrew from Jerilderie