Another thought you might try:
A clock or watch might help you if you really don't know.
If, for example, you descent 700 feet per minute to the threshold.
It would take you a bit more than two minutes to get down from 1600 feet.
If you time your traffic pattern next time you could figure out when to start your descent.
If you prefer 500 feet per minute, start descending 3 minutes before landing.
Try this a few times and you'll learn how long your pattern is time-wise.