What is the ruling on one who delays performing ghusl until the time for Maghrib prayer has expired, despite intending to perform it before its time elapsed?

If ritual bathing (ghusl) was obligatory, then there is no sin upon you for completing your purification and prayer, even if the time for it has elapsed. However, if the ghusl was for cooling off or cleaning, and you knew that the time had expired, then you have sinned and must repent. But if you thought the time was still remaining and were then surprised to find it had expired, we hope there is no sin upon you.