Hi Bob -
They don't get any easier than this car. If you take your time, do a thorough job, have a coffee break, and it's you first time, then it *might* take 90 minutes. Seriously, I know folks who have done this job on their lunch hour.
Be certain to get a good quality replacement pump. The chain-store-cheapies have an impeller made of stamped sheet metal - don't use one of these, whatever you do. The dealer is actually a good bet. Last I checked, an official MB rebuilt water pump listed at $25. Guess I should put in a plug for Partshop too - they have a couple options from $32 to $53.
I like to use a copper based gasket sealant on the water pump gasket. I find they never leak upon reassembly when using this stuff. Also greatly eases reassambly - it dries tacky, so can be used to hold the gasket in place while you put it back together.