kgiloo - This appears to have been fixed in 2.0.18. I just checked and that is the version we are currently on and see that it is set to scan every 30 minutes. I think the other issue with Bitbucket Webhooks was also addressed, so everything seems to be working for us. Can you check on your end?
Jenkins 2.107.3, Bitbucket Branch Source Plugin 2.2.11, Pipeline multibranch 2.19 and branch api plugin 2.0.20 are doing the same thing for me. No mater what I set my Bitbucket team to the downstream multibranchs are stuck at 1 day with no way to change them.