The first four hours of the day go to the hardest thing on the list. No calls, no email, no exceptions I have not planned in advance.
Afternoons are for other humans — client calls, reviews, the messages I owe people. Batching it means nobody waits more than a day and nothing interrupts the morning.
Evenings are for training and reading. If a project starts eating the evenings for more than a week, the project is mis-scoped and that is my fault, not the client's.