It's pretty easy to get up to 93-95. After that, you'll need to put in titanic work and/or have a team that sets things up for you.
Periods For Levels In Baal Runs (If 1 baal run = 4 mins)
89-90 = 40runs = 2hours 40mins
90-91 = 60runs = 4hours
91-92 = 80runs = 5hours 20mins
92-93 = 120runs = 8hours
93-94 = 180runs = 12hours
94-95 = 330runs = 22hours
95-96 = 550runs = 37hours
96-97 = 1000runs = 67hours
97-98 = 3000runs = 201hours
98-99 = 9000runs = 603hours
Note: those numbers may be a bit outdated, you can get to 99 in like a month now on ladder (with a dedicated team, ofc) since the runs can be faster and more optimized with Nihlathak+Diablo etc.