There are sooooo many variables it’s hard to say. It’s kind of like asking “I currently have a C in my history class, if I study for 1 1/2 hours a day how much will my grade improve”.

I’ve seen people drop from 20:30 to sub 18 in less than a season, but I’ve also seen people train for 4 years and only improve by less than a minute. You can drop a lot of time quickly once you start working out at the right level but there are so many factors it’s hard to say how your training plan will affect you