There will never be a guarantee of upgrade time, however, given the experience levels of new hires at the moment, they’ll be a long time in the RHS.
6-12 month commands in the regionals are not unheard of for those joining with experience, but only because they were “the most senior applicant with a valid bid”.
As the current Captains move onto Jet and the Senior FO’s replace them there will certainly be a shortage of FO’s meeting the experience requirements to upgrade thus commands will go below them.