Once you kill all the tadpoles, if you roll towards Deku Toad he will jump up straight away rather than waiting for him.
If you C-Up while Deku Toad is in the air he will fall down immediately.
When Deku Toad falls down he will always face the center of the room.
All of the bomb strats below work with normal bombs, not just water bombs (except that you cannot use a normal bomb to blow up the tongue on the ground in the same way).
At the start of the fight, immediately shoot a bomb arrow into Deku Toad's mouth, then shoot another bomb arrow at its mouth as soon as the tongue fully hits the ground. For the second phase, rinse and repeat.
The normal strat for the Deku Toad one cycle with bombs has you kill the tadpoles and wait for the toad to fall down. It is possible with precise timing, however, to throw a bomb into his mouth with the boomerang at the very start of the fight, skipping this process and going straight into the knocked down portion of the fight, saving around 15 seconds.
To do this, make sure you have bombs and the boomerang equipped when entering the room. Skip the cutscene, and while the game is loading the fight, hold ZL, up-right on the control stick, and whatever button the bombs are on. This should buffer targeting the toad, walking a little to the right, and pulling out the bomb on the first frame, respectively. Then a few frames after the game loads, tap the boomerang button (you can also mash) while continuing to hold ZL. Link should throw the boomerang and the bomb should go into Deku Toad's mouth. The window for the throw is tight (only around two frames), but thanks to input buffering, it's only one tight window and not several.
The rest of the fight is the same as the normal one cycle with bombs fight.
At the start of the fight, go behind Deku Toad and kill the tadpoles quickly. C-up so that Deku Toad falls down, then place a bomb next to its tongue. You can either slash the bomb (but be careful not to hit the tongue), shoot it with the slingshot if you have that, or wait for the bomb to blow up. Then throw a bomb into Deku Toad's mouth and repeat the process.
Without bombs, the fastest way to kill Deku Toad is with two sets of ten well-timed non-combo slashes. The sets of ten can be broken up into either ten individual slashes or five sets of two slashes. Just make sure not to do a full combo.
It is easier (but around 0.2 seconds slower per cycle) to do the following combo: jump attack, then four individual slashes (either separately or in two sets of two), then a full combo. This is the same combo used to deal damage to Beast Ganon.