Timesheet Application for Mac?

I am looking for a simple application that will:

1) Let me use a timer -OR- enter start and end times.
2) Automatically calculate the hours in another column.
3) Recognize my parameters for grouping days for totals (weekly total, and pay period total for 1st-15th and 16th-31st).

Any ideas of an app like this? It could be on the iPhone too, as long as I can backup the long-term info on my MacBook Pro.

Thank you all in advance for your help!

Peace,
Jason