How long do I have to wait before bandits take over Helgen Keep?

I recently started a new playthrough of Skyrim, and I want to get the archery skillbook in Helgen Keep. According to the wiki, that skillbook doesn't show up until bandits take over the keep. How long do I have to wait (I just completed "Unbound") until that happens, so I can kill the bandits, get the skillpoints from them, and get the skillbook?

Solution 1:

The Helgen entry on Fandom is - as is often the case - not particularly clear about it:

A few in-game days following the events, a small group of bandits will occupy the ruins of the town (the lock on either gate must be picked, or one of the bandits can open it).

But on the Gamesas forum some theories are proffered, among which:

• I just took a quick look in the Creation Kit, and it seems like all you need is to have visited Whiterun at le[a]st 4 days [?] after escaping from Helgen.

• [The bandits] respawn every 3 in-game days.

More ideas can be found on the UESP discussion on the topic, and having to finish the Dragon Rising quest shows up again. However, that quest requires you to visit Whiterun, so just the visit could still be the requirement.
In fact, this is corroborated by its last entry:

The bandits take over after you visit Whiterun (marking it discovered on your map, you don't need to finish or even start Dragon Rising), you don't need to wait for a cell reset to trigger the first bandit occupation.

I currently don't have Skyrim installed or I would have tested it, but this seems credible: visit Whiterun and return immediately (or possibly wait for 3 in-game days).