It takes more effort to start a project than to do it.
Once I’m at the sink washing dishes, it takes the same effort to wash two as to wash twenty. The momentum carries you forward and the repetition can be done mostly automatically. It’s the shift into “wash dishes mode” that takes the most cognitive effort.
(This is one of the reasons I prefer a smaller number of longer workdays, too! Any day that has work in it is a “work day,” regardless of length. A ten-hour day doesn’t feel different to me than an eight-hour one, but an extra day off is great!)
So do things as you go. Wash one dish on your way through the kitchen. If that’s all you do – hey, you’re one dish cleaner. But chances are you’ll find that once you’re over the initial hump, those dishes (or laundry, or emails, or whatever) will fly by once you’re in the mode. And the mode is easier to switch to if your initial cognitive commitment is just one unit.