Lillesort131: Well, the most likely reason for the wait is probably that they are testing the patch to see whether it breaks anything / is otherwise dysfunctional. I would rather wait a couple of days and be sure that I actually get a functional version than download it instantly and realise that it have some data-corrupting bug that erases some of my files. Also, what if someone hacks into one of the developers machines / steal their passwords in some way? Then, if the updates were to be released directly, we could get any kind of malicious software.
Disclaimer: I don't know what they actually do / how their update process is. If have written this with the assumption that they actually do some QA testing on it.
Developers, Squad in this case, does that. Not GOG. If Squad already published the patch, then it's pretty much all okay. All GOG needs to do is to upload it to their servers or a similiar process and that shouldn't take 3-5 days or even more perhaps.
Hacking into developers machine and giving users malware because of instant updates? Not sure if you're serious about that part but it kinda sounds ridiculous, no offense.
At this point, I wish Squad would release the game updates on their website as well, to avoid this kind of situations.