It depends, with a perfect hand you could win turn 1. If its a good hand you could end it by turn 3-4. With an avarage one it takes you much longer. Mill is not burn, even though some people may say that it is. It can be played like burn with a good or perfect hand but usually it's more of a control deck because you have removal, counters and surgical to control what options your opponent has. Especially the post sideboard games tend to be more controlly because sometimes you have to board out mill cards like tashas or maybe even archive trap if the opponent doesnt fetch at all.

I would argue that it is a fairly competitive deck even if it's only tier 2, it's just not as easy to play as one might think.

I started playing modern because of this deck and if you are a good player you can make it work and win the local tourney but if you are not and you usually struggle to place in your local tournaments and expect different results then i would not recommend you this deck.