Ferber worked but it still takes so long!

We started sleep training our almost 6 month old about 3 weeks ago, and Ferber worked like a DREAM! The first night took about 45 mins, night two took about 25, and then most nights after that took less than 10 minutes with minimal fussing. Still the occasional intermittent crying, but more often than not he would settle himself within 5 mins!

Over the last week though it feels like he’s taking longer and longer, maybe 15-20 minutes? And he’s crying a lot more than he did initially. It’s still more of an intermittent cry and he is still self soothing, but it’s a regression from how things were after the first couple of days.

Am I doing something wrong? Bedtime used to be around 8 but this past week it’s shifted to 7:15-7:30 because he’s been waking up earlier and earlier. Wake windows are 2/2.5/2.5/3 but he doesn’t seem that tired at the end of the day? Should I be keeping him up longer than 3 hours? I don’t want him to be overtired! Nighttime routine has stayed the same, bottle, bath, bedtime story and then bounce/rock for 5 mins before putting him in the bassinet. He’s started crying at the end of his rocking before I settle him and will cry in the bassinet before I leave the room, preciously he would go into the bassinet fine but then start crying a minute or two after I left. Now it’s right away.

If anyone has any advice that would be great! Not sure why he’s regressed a bit or if that’s normal?