The two days part is probably due to them wanting to have the engine ' stone cold'...which is proper... with practice and the proper tools and no surprises...it is a couple of hours...
Of course you posted on a forum which leans towards doing it themselves.... tools are a one time cost... but you will need regular setting of the valves... so the longer you have it the more you will have saved... leaving off the fact that you will know exactly whether it was done correctly ( hopefully ).... LOL