After the "Seven Years" arc in Fairy Tail, the Celestial Spirits throw a party for Lucy and her friends, and when they leave, they discover that 1 day in the spirit world equals to 3 months in the real world. If that is so, then 1 and a half hours in the real world equals 1 minute in the Celestial world, so how do Celestial Spirits have time to recover?
For example, in the "Seven Years" and "S-Class" arc, Lucy summoned Taurus to fight the voodoo doll guy and he gets annihilated, but then she summons him to fight Hades/Precht and he was fine. By my calculation, he had maybe 1 or 2 minutes to recover before he was back in the fight.
Side note: this also means that Loke was banished for a whole whopping 12 days and everyone on Tenrou was frozen in time for 28 days in the spirit world time.