well, the splitter thing is probably a diplexer, and a flawed diplexer would not affect the whole system. i wonder if the tech replaced the power inserter when he replaced the switch. but anyway, your issue would be at the switch or before, or with the power inserter. other wise the signal loss would not affect all receivers. are you SURE he replaced the lnb's? there should be 3 duals on there and NOT an integrated lnb. and the cables should come from the dish, go to a ground block (which should of course have a green #10 ground wire to a proper source) , and then to a switch. otherwise the install is flawed.
there are frequencies that cause interferance. i would look into what is happening at that time of day. is your neighbor pulling in from work, parking near your dish (on-star has been said to cause interferance issues). is the switch mounted somewhere where it gets lots of sun (hope its not on the roof!)
i dont know, but if i were the tech, i would be embarrassed that i didnt fix it on the first 2 tries, and would probably rip the whole thing out and re-intall it at this point. if it didnt work after that...then its not going to work.