70% of heat loss is from evaporation, which is why the cover works. The point of covering at night is that is when there is the greatest difference between the water temperature and the pool water and the most evaporation. For the two days you are swimming, you should cover it up at night to keep the heat in. I leave the cover on my inground pool all day during the summer if we aren't swimming so I don't see a problem with that, as long as you aren't shocking. I have had blue and clear covers and I think the clear helps a bit more to generate heat, but it may be in my head!

If you do this, it wil be an interesting experiment and let us know how it goes, particularly with an AGP with the side exposed to the air and less water volume than an inground with a deep end for diving.