Short term activations?

I’m scratching my head about a way to get ST to do something and was hoping for some help.

I’d like be able to - on an adhoc basis - tell ST to activate a smart plug (with heater attached) and run for one hour, then turn off. And to be able to each time choose whatever time it comes on (or preset multiple choices.)

If that sounds a little muddy, basically I want to warm one room of the house before I get up - but I won’t know until the night before if its needed, and I get up at different times.

I was thinking that a number of routines (set for say 4am, 5am, 6am etc) would make sense as I can activate that through Alexa or Android widget the night before. But I can’t wrap my head around how to make it work. Any ideas?