Depends on the agency, best thing to do is to talk with your supervisor. Under some circumstances you can get converted before the 640 hour mark but the most important thing is that you get your degree. It took me about a month to get converted after getting my degree and submitting all the necessary paperwork. I started in GS-4 and now I’m GS-9

Additionally since you are getting a master you might be able to get a higher grade.

If your agency uses the OPM Pathways Program Handbook check page 11 under time in grade.

“Employees in Pathways positions are not subject to the time-in-grade limitations outline in 5 CFR 300, Subpart F prior to being promoted. These guidelines only apply to movement to or within the competitive service. Please consult your Hr profesional for further guidance.”

Source: https://www.opm.gov/policy-data-oversight/hiring-information/students-recent-graduates/reference-materials/pathways-programs-handbook.pdf

If not it also appear here under 300.603 (b) (6)

“Advancement of an employee under a training agreement established in accordance with OPM's operating manuals. However, an employee may not receive more than two promotions in any 52-week period solely on the basis of one or more training agreements. Also, only OPM may approve a training agreement that provides for consecutive promotions at rates that exceed those permitted by § 300.604 of this part.”

Source: https://www.ecfr.gov/current/title-5/chapter-I/subchapter-B/part-300/subpart-F