when to go from blowoff hose to fermentation lock

hello all! I'm new to the forum and homebrewing. I've just started my 1st beer, an IPA, and attached a blowoff hose. I've read alot, and i'm sure I sound pretty neurotic, but when should I replace the blowoff hose with the fermentation lock? I've seen: when the activity/bubbles start to slow, generally around 2-3 days. is there a good rule of thumb to know when? sorry, if this has been addressed elsewhere, I did not see it. thanks so much for your help!
c

Pull it off when it stops sending krauesen through the blowoff tube. Not really a measure of time, but rather of utility. Just remember to keep everything clean and sanitized.

You can put the airlock on as soon as your Kreuzen starts to go down. Its really all about the headspace. If you've got some after that initial active fermentation starts to subside a bit after couple days or so, chances are you you aren't going to clog the airlock with any schwag.

Personally, if I am going to secondary the beer (for dryhopping or high graviy brews), I just wait until then to go airlock.

Hope that helps.

I really only use one if it is needed. How big was this beer, and how much head space do you have for the krausen?

I put my apfelwein on blow off for 1.5 months without changing the water... I just bottled it yesterday and noticed the mold in the blowoff water... wein tasted ok, so I guess I lucked out this time...
Next time, I'll switch over after 1 week.

BTW... I used Notty, that's why I used the blow off.

thanks for the replies! I think i have enough headspace(i'm actually a little concerned I didn't fill the carboy (5gal) up to its 5 gal limit.) But I think I'm gonna wait til the kreuzen begins to go down, maybe 1 more day. if I somehow didn't fill it all the way to the 5 gal limit, should I consider using a bit less the 3/4 cup corn sugar for the priming solution, come bottling time? thanks for the help
c

If you're fermenting in glass or metal, you can change to a 3-piece 'compact' type airlock, or equivalent, after 7-10 days.

But, if you are fermenting in plastic, then NEVER change from the blow-off tube...unless, of course, you enjoy vile 'suck-back' solution in your beverages.

Just MHO, of course.

Pogo