For many babies the cluster feeding stage starts early on, usually in the first two weeks of life and can go on until 3 - 4 months old. (breastfeedingneeds.com)
And according to experts, while not every single baby cluster feeds, many do. (romper.com)
All other things being equal, I would guess that the best time to power pump is probably early evening, since that's when babies cluster feed (and you want the pump to imitate your baby as much as possible). (exclusivepumping.com)