It sounds like you live in an ideal world. I often help different clients in the same day. Website bugfix in the morning, bring up bluetooth in the afternoon. It's hard to say ahead of time how long either task will take.
Am I supposed to look over my commits at the end of the week and guess a weekly amount for each client? That sounds awful for everybody.
Sometimes you can bill weekly, sometimes you need more granularity. (I use hours.)
I believe part of the idea is not to take on jobs that are an hour here or there, but to take on work that requires full days or weeks. Your daily/weekly wouldn't change from customer to customer.
Am I supposed to look over my commits at the end of the week and guess a weekly amount for each client? That sounds awful for everybody.
Sometimes you can bill weekly, sometimes you need more granularity. (I use hours.)
And, no, I'm not doing it wrong.