It's not the time available to an angler, but the nature of the rivers and the SPECIES of mahseer - mostly Barbus tor putitora, the Himalayan Mahseer, very different and wider-ranging animals than the sedentary Tor Mussulah fatties of the Cauvery in the South. You have to find the fish (they might be "gone" - fifty or more miles away), and, even then, if they're in front of you, if the river conditions aren't right...
There lies the challenge of fishing for BIG North Indian mahseer - being in the right place at the right time (as well as, of course, doing all the right things), and knowing that some years you cannot be (early / late monsoon or the fish not holding in their usual spots...). So you get big-time failures (not something that commercial operators could live with, whole, in some cases, just 2-week-long "season"s / windows blowing out), but a few continue to try .... and when you get it right...
A 71-pound mahseer from a Northern river is my recent-years best (I won't better it), after two total blow-outs...