It's 2 tickets for a win, 1 ticket for a draw, 0 tickets for a loss so just halve Solidddd's calculations (they seem like fairly good calculations) and that could be around about how much time you need to spend.
Of course, if you're a higher level or when you've played a few more games and gained a bit more experience in castle wars games, you *should* be able to win more than half your games which will reduce the time it takes. This could be done by maybe joining a higher level castle wars clan or just picking up on strategies and do a one man show in ur castle wars game