We encourage people to track time as it is done or at least the same day. They can do it at task level or on the timesheet. If they leave it any later than the same day it might not be accurate.
Basically the same as @Heidi Stephenson‚, but we still have people who enter all their time at the end of the week or even the end of the pay period.
Same thing as @Heidi Stephenson‚ and @Kevin Quosig‚ We also do a drawing every Monday for a $25 gift card. Everyone who entered all their time for the week previous by Monday morning gets to go in the drawing. We've had great activity for the last 3 months of doing that!
In case you're looking for some extra oomph to make time tracking even easier, I invite you to consider:
Our Enterprise Stopwatch solution can improve and expand your users’ adoption of Workfront by making it simple and convenient for everyone to track time from their browser, tablet, or smart phone, as the work occurs.
Our UberTimesheet solution is intended for capturing time after the fact, and -- although similar to the native timesheet -- includes extra features such as a Quick Filter that instantly shows only the Timesheet rows that match a particular search string of interest as it is typed, and a Time Spreader feature that will evenly divide the time entered at a day level across all of the selected Timesheet rows (i.e. for execs and busy PMs).