the only problem here is that once you either do your override or the increase, as soon as it has reached the temp it then goes back to normal. In my opinion not good. If its really cold then you may have to do it again. Not a problem if it once but what about three or four times.
Why not have a heating boost function, that you can say once new temp has been reached maintain for 20 minutes or 30 minutes, Or have temp boost 30 mins and temp boots for 60mins.
I think 0.5C is not enough, most people won't notice a half degree drop needs to be whole degrees.
Occupied and unoccupied. I've done this with an x10 system. Basically the heating is programmed like this
ON 07.30 Off 08:45
ON 16:00 Off 22:00
ON 07:45 Off 09:00
On 16:00 Off 23:00
heating on temp is 22C off temp is 15C
Then we did when house is empty use 17C when heating is on. The when house is occupied set ON temp to 22C
Works quite well.