1) Once you kill all the tadpoles, if you roll towards Deku Toad he will jump up straight away rather than waiting for him.
2) If you C-Up while Deku Toad is in the air he will fall down immediately.
3) When Deku Toad falls down he will always face the center of the room
Having the early boss fights flag active has an interesting effect on Deku Toad. It may seem like the fight hasn't started early however what it really skips is the cut-scene where the vault shuts behind Link and fish fall down before you C-Up to start the fight. While this may not seem like much it actually allows the fight to be started from the door where you normally exit because Deku Toad is already on the ceiling, you can then simply look at the ceiling from behind the gate and you will be transported into the fight. This means we can beat Deku Toad without the Water Bombs required for the rock that blocks the tunnel to enter. This Saves 37 seconds in Any% and 7 seconds in All Dungeons.
When doing early Deku Toad you won't have water bombs to one cycle him. However it is possible to do 10 slashes with the Master Sword which is enough to kill him. You want to stand next to the tip of his tongue to minimize the time it takes for your sword to hit him, the timing is also slightly tight as you next to do each hit within 3 frames off the previous hit otherwise you won't be able to fit in 10 hits.
If you have water bombs it is easier to 1 cycle Deku Toad than having the Master Sword alone. A water bomb has the same damage as 5 Master Sword hits so you will need to hit him 5 times with the Master Sword and have the bomb explode shortly after. To do this pull out a bomb as he falls down and hits the floor, you will also want to place the bomb in such a position that you won't hit the bomb when slashing his tongue.
In 100% you can do 5 slashes with the master sword then finish him with bomb arrows. Quickest method of killing Deku Toad. The slashes are not precise