If my summoned creature will take an hit, can I heal his wounds using spells or potions?
If the summoning time is more than 24 hours, the creature will recover hit points resting at night?
1) Yes, unless they are undead, then you have to inflict.
2) Yes. But thats probably a calling spell, not a summon.
Mount is a summoning spell, and the light horse conjured can stay for more than 24 hours starting from 13th level.
I said probably.
Specifics like these are best left to your GM to be honest. Too many circumstances to be considered and without knowing the game you are in hard to say.
Why do you think you can't?
I said probably.
Yeah, but in case someone else had you doubt, I brought the example of a summoning spell during more that 24 hours.