When traveling through a door transition, the game will center the door on that edge of the screen before bringing it across the screen to change rooms. This does not increase In-Game Time but does add to Real Time for runs. As such, RTA runs should make the effort to align the door transitions to the middle of the screen whenever this would not negatively impact the movement in the following room.
A normal door transition is 42 frames, though there might be processing reasons why this would be higher even with a perfectly aligned door. Both processing time and door alignment time will be reflected in the number given by InfoHUD.
As shown in this example, entering the door to the far right creates a door transition of 101 frames, nearly a full second slower than if it were perfectly aligned. The other example has aligned the door such that the transition takes 43 frames, only one frame slower than perfect.
There are some door transitions where some strategies align the door, while others do not for the sake of the movement afterwards. These include the door transitions between Green Brinstar Main Shaft and Dachora Room, between Single Chamber and Double Chamber, and between Speed Booster Hall and Bat Cave.
One notable transition where runners do not jump through in order to align the door is going from Big Pink to Green Hill Zone in the early game. The standard strategy relies on the run speed gained before the door transition in order to jump and perform a mockball on the level below.