"No force can harm it" "Its physical condition becomes fixed." The wording is such that temporal stasis only affects the creature, not the spells affecting the creature. Since the spell that summoned the creature is not put in stasis, the duration continues to tick down.
When it reaches zero, it stops sustaining the existence of said creature. Stopping the sustaining force enabling a creatures existence is not an attempt to harm the creature, it's merely an expiration of what causes it to exist.