This is not the case. The feature will turn it self off after searching for 90 seconds without finding enough players within the given range.
However, in the next version of MM change, we will make additional adjustment to make matchmaking speed a little faster.
Over the last week or so since the changes I've just seen the game go downhill so fast...
....so much that I am not even doing games with other people and have just switched to AI games due to the bad play, trolling, general imbalances in the matchmaking games, etc.
I don't find games fun where one side just destroys the other because you get paired with 1-2 players that aren't close to your skill level and they get dominated and it snowballs the game...even though you've done your job or held your lane in a draw.
There is something 'fundamentally' wrong with the system...it's obvious.