I say, and with God's success: The voluntary prayer is recommended at all times except during the times of dislike, which are at sunrise, sunset, after the Fajr prayer, and after the Asr prayer. The prayer of gratitude is one of the voluntary prayers, and God's blessings upon us are many. Whoever wishes to pray it at any time is allowed to do so, thanking God for the goodness He has bestowed upon him. And God knows best.