Guild-join block seems buggy

Hey, I have noticed and read different things about the block you receive when leaving a guild.

Now I left a Twink guild with my bard to join the main guild.
The bard has not been in any other guild prior to that and has been in the guild for over a week.
I did donate to the twink guild after the daily reset and then left, expecting a 24h block.
The notification already informed me that the block will be in place for 4 days.

Now I am wondering, why is that? Another mate just recently left the twink guild to join the main guild and only had an 24h block.

What determins the timeframe? It seems a bit random, or buggy, which is why I am posting this here.

Please clarify. Thanks a lot.