If I run the following...

task = RunScheduledTask[MessageDialog["What do you want to do?"], 5]

...things seem to work fine.

But if I run...

task = RunScheduledTask[ChoiceDialog["What do you want to do?"], 5]

...Mathematica hangs, presumably because of something to do with MessageDialog[] not returning a value, whereas ChoiceDialog[] does.

Does anyone know of any way around this? I have tried wrapping ChoiceDialog[] in a function which itself returns nothing, then wrapping that in RunScheduledTask[].

But what I really want to achieve is to run a scheduled task that asks the user whether they want to do something or not, so I am stymied.