If it's not that important why do they time them at the combine?
It's not that there is no importance. The biggest thing it helps do is normalize the game tape b/w prospects. Say you have a guy who is blurring past his opponents and throwing them like rag dolls in FCS compared to a PAC 12 players who doesn't appear as fast compared to other players and isn't able to move them around as much. You know the FCS player is going against inferior competition, but how can you compare the two?
You have the combine. There, you find out that the FCS player did 27 reps on the bench and broad jumped 10'3 compared to 19 reps and a 9'7" broad jump for the PAC player, but the PAC player ran a 4.48 and the FCS a 4.57. Now you can see the FCS player is indeed stronger, but isn't as fast in a straight line when comparing the tape of the two.