there is a very easy solution , and is also my way of farming jarl..........for high level alt, just do "/partyinvite 000" and "/partyleave", i use to copy and paste the first command and type the second, this is more efficient than you join a farmed map or almost farmed map.
For low level alt, just join a game, kill and run to boss, because low levels cannot kill jarl very fast, u will always be on time.