So let say if i join a group and giving out 6min Haste II is that like a "omgnoob Rdm we wont invite him again" kinda thing?
No, nothing like that.
It does depend on what the group is doing though. If you join a group aiming to clear v25, the expectation is that everyone in the group has their respective job maxed out. In that group, you do
need 12-14min hastes so you don't have to re-buff everyone mid fight - Ody fights are 15min long.
If you're joining a Limbus/Ody/Omen farm, there is no such expectation.
For rdm specifically if I saw someone with a 6min haste2 I would think they're new to rdm. Duration for others is pretty easy to get for rdm, literally 5/5 empy will get you most of the way there without having to upgrade relic/af and you just keep improving on that incrementally.
I would not ask them to do anything like land debuffs on HELMs, sortie bosses or Dyna NMs, but good people are always invited to things appropriate to their level regardless if they are new to the job or not. It's more about you taking feedback, willing to improve and honest about what you can/can't yet do.