Have no idea what you're doing -- about 4 hours.
Have decent mechanical skills -- 2 hours.
Have assembled a SC-10 suspension from a box of parts & know exactly what you're doing -- 1/2 hour.
It took me longer to figure out what they were trying to tell me in the instructions than the amount of time it took me to install the kit.
Basically unbolt rear axle adjuster blocks, replace bolts w/ longer ones & put aluminum plate on inner side of rail. Unbolt upper rear suspension arm & jack up back of sled. Remove idler wheels & take out spring spacer, cut 1" off, install spring spacer, ets arm, ets washer, idler, idler shim, bolt rear arm back in place in the tunnel, check track tension & alignment.
They also give you the recommended suspension settings, so you may also have to change your shock settings & limiter strap length.
There's also decent article on www.snowmobile-online.com in the Info & Tech center.