Time skip basically a skill that you use once in a while and that takes resources to execute properly to increase pacing of the story. Those resources are immersion, expectations, and detail. It also is in telling category, so if the story before was all show and suddenly time skip, it breaks the immersion. There are constraints in which the time skip works the best, if it's justified, if it's logical, if it's emotionally true afterwards.
Justification is your reason to make time skip. Self explanatory so far. The reason "why" this timeskip exists will be judged by the reader, even if that time skip is small. The bigger the timeskip is, the less it will be justified, because people change a lot in years than in days. For example: a year timeskip because of training montage feels different than 10 years training montage, even in if narrative wise they're the same montage session. If you make it 10 years, you don't just make MC punch better, you make MC capable of crushing boulders with a single finger, aka managing expectations through the inner logic of the story, logos.
Justified time skip is logos (here's why time was skipped) + ethos (here's what you expect out of it) mostly. Emotional aspect is after you've made your case to the reader, and show off the changed connections between the people, which is detail. Time skip compresses detail to the point where it only can be told through telling if you want the maximum detail shoved down as possible on what happened between that time period. It feeds off of the context of what happened before the time skip and expectations that leads to the time skip.
How those previous connections are established constrain what will happen logically in the future, so if the reader is already invested and roots for the characters, it's often negligible until you break your own logic. Those breaks of logic scrutinized the most after the time skips, so think accordingly.
It's not the matter of an arbitrary number, it's the matter of "if that number you've putting out there makes sense to the reader". Often, writers forget that time skip breaks or makes the story and it's a skill you can overspend without realizing. I can list a few where arc ended + timeskip broke the story for me specifically, like Souma, Bleach, and Tree of Aeons (don't ask). That's all.