Altho they all wear down at some point, it took me maybe 10 mins/side to recently replace both in my 450...but I've also had to replace the engine, and the cab has to come off--that took a little longer.
Replace both even if one shows to be ok. Get some good ones, having them run down is a hassle.
'16 40QBH Phaeton
'15 38RSSA Mobile Suites--traded
'05 36TK3 Mobile Suites--retired but not forgotten