I just bought the Ultimate Edition and reached the Online part of the game. Its been 20 mins so far and its still “Matchmaking in Progress” for 2 orange events I tried. How long does this take?
a lot 
It depends on how many players are online on the servers you are connected to (the more players, the more probability they will want to play with you), on your region (connection latency and total number of available Forza servers).