I'd like to be able to estimate how much time a task will take in order to better plan my days. Can I do that?

You can. Task Time Estimates are enabled by default in Daycast. To use this feature, include an amount of time in your task descriptions along with either the tilde, greater-than symbol, or less-than symbol to indicate approximation, minimum duration, and maximum duration, respectively.

Daycast will notify you that you've reached your estimate when the amount of time clocked against your task equals the amount of time specified in the task's description.