Is Asher Yatzar said after using the bathroom in the middle of the night or does one wait until the morning to say it?

Shulchan Aruch OC 7; 1 writes that Asher Yatzar is recited anytime throughout the day. The Mishna Brura 4; 3 brings a lenient opinion that one can rely on the morning Asher Yatzar, but that is applicable only if you don't need to go again in the morning and therefore concludes that one should wash his hands three times with a vessel and say the Asher Yatzar every time after using the toilet at night.