from my own experience things tend to reset after 24hrs
BUT... if you downloaded near your limit let's say the limit is 2500 & you downloaded 2300, you may get the "unusual activity" much sooner than 2500 the next day. if you continue to download after that unusual activity warning, the path to getting blocked is greatly reduced so there is also a factor of how much you abuse your privilege to download without consequences. This is why i try to login to my account after a bulk download to see if it triggered anything. Sometimes i just download small profiles & get that warning so it may be because things i did in the last 48 hrs. Getting a "clean slate" is a good place to start if You are trying to find a balance when the rules are not clear. You have to test the waters yourself & risking a block which will be temporary the first & probably second time.
It's quite funny but you may think of it like a thief breaking in & taking stuff from am apartment. If you take too much stuff someone may see you loading all that stuff. If you take fewer things but stay there for too long coming back & forth you may also get caught. If you come there the next day you greatly increase to chances of getting caught.
Instagram has pretty smart web developers so it's not that simple to find the sweet spot.
my methodology went like this...
I personally started with downloading big profiles. I know for a
FACT you won't get to 5000 images\videos in a single session without getting flagged as i tried to download a profile with 5400 several times & never achieved it.
This is also bandwidth dependent , getting as much as you can as fast as you can will net you the highest "yield"
so first figure out roughly how much you can download in a single hit (you will get notified that downloads has stopped working)
then wait idealy for 48hrs dial it back & try again. you will find the limit this way & for you it may be diffferent from me, this is why you need to test it yourself.
get a number you know is safe to download for 48 hrs.
Take that number & try again with 24 hrs delay.
you also need to see the size of the downloads since some profiles are more video heavy.
let's say you came up with 1200 files & 600mb the next thing is to try again the next day & if you are not getting the unusual activity warning then you have found that limit.
If you don't want to bother with all the above you can just choose profiles download them one after the other until downloads stops. then wait 24-48 try to login to with the steps required to activate the account again. wait another 24-48 hrs so you won't get instantly banned again then bulk download again until getting blocked. If you do 2 serious violations within 24 hrs then you may risk losing the account or getting banned for more than 48 hrs.
Single posts change the rules because it's harder to check for "rules" that way. also it's alot of work that way & missing the point. you may aswell use web based solutions.
the thing is that you are risking it even by downloading single posts because you will eventually get noticed, there will be a limit to that also which i did not check so in this case you have to figure it out yourself. for me i prefer to download 1-3 profiles every 24-48 dependent on warrning , amount of content (above or below 1gb) , the amount of time it took to download them. trying not to exceed 2500 files unless i'm willing to take that 24 block.