Being creative on a deadline is a different muscle than being creative when you feel like it. Train both.

Working to a deadline and working when inspired use different capacities. One asks you to produce on demand with whatever happens to be in your head, the other asks you to recognise an idea and follow it, and being good at either does not make you good at the other. Relying only on mood means missing most of your chances. Relying only on deadlines means never making anything nobody asked for.

Train the one you use less. If you only work when moved, set yourself a dated task, and if you only work to deadlines, block an afternoon with no brief at all.