Some random design thoughts just for seeing a complete picture, if you don’t mind:
1) have you tried different intervals, let’s say every 5 min instead of 1 min?
2) have you tried to actually draw a smaller font clock? Does it affect the battery? I mean, fewer pixels, less power, right?
3) have you tried to lower cpu clocks before going to suspend? There is a project by knc1 about manually
lowering cpu clocks on Kindles (Kindle response gets slower of course, but in your case this would mean probably slower redraw times and longer time to wake up). Not sure if it works with PW4