I keep a recipe box next to Eddy's cage with 3X5 note cards inside. I write down the date and whatever information(amount fed, regurges, sheds, etc) is relevant at the time. I also check his weight and length periodically and take a picture of him at the same time and put it in with the cards so I can see how he's progressing.
As for your scenario, if I fed on Thursday night, I'd check to be sure he's poo'd on Sunday, then if he has, I'd feed on Monday night or possibly Tuesday(depending on what my schedule allowed). If he poo's on Monday, then I'd feed Tuesday night.