I would agree with Vince. The knowledge gained in a studio setting vs. online would be incomparable. I also agree that a pay hike is not likely unless, A) Your employer is encouraging you to do this and agrees to pay you more upon gaining your Masters, B) You look for employment elsewhere.
FWIW, I am currently a full-time architecture student going for my BSAS, and then immediately for my M. Arch. I was on this forum for a few years before going to school, and while the skills that I learned here were of value and worth, putting myself into the pressure tank of a studio setting helped me grow exponentially from where I was prior to school. I reacted well to that environment, perhaps yourself or others may respond better to an online setting. For me, the intense but typically friendly competition from my peers pushed me to ramp things up. Plus, these friends will be valuable contacts in my network as I grow in the field of architecture. I work full time to support myself while I am a full-time student and there are times that my school/work/social life is challenging to balance, but it's all well worth it!
You're young [alot younger than me ], so go for it!
Best wishes!
Paul