You can just enter it in the Due field; "tomorrow at 1 pm" would work just fine.

More examples of the different formats are on our Help page.

Can you enter a specific time if you are also entering a date? Eg, if I want to enter a task on 8 June at 9.30 am it sometimes works but it sometimes messes up myh due date. Whereas if I just write today or Monday or Thursday at 9.30 am it usually gets it. Any thoughts?

Catherine,
This should work fine. If you're getting any times that aren't parsed correctly, would it be possible to submit a Tasks & Lists issue report via our support system?

Please select the issue that you're experiencing from the list on the left, and follow the steps shown. If your issue isn't listed, just click on "I'd like to report a new issue" on the left.

Your report should provide all the info that we need to investigate further, but we'll be in touch via email if we require any more details.

Thanks!