Best shot is on the night of the 5/6th. Somerville had information on the Japanese from the afternoon and from that he predicted they would be somewhere just to the south of Colombo or turning west of it during the night. Unfortunately Nagumo had reversed course. Nagumo had no clue where the Brit fleet was, not finding it where he expected. Somervilles night search with radar equipped aircraft found nothing & the strike of torpedo equipped Albacores remained on deck at dawn. How much damage 30 to 50 Albacores doing night attacks with torpedoes could do is a tough one to estimate. Somerville had rehearsed such a attack a few times in the preceding weeks, & the attack on Taranto had scored a lot of hits, but this would be against ships taking evasive action at speed & at night. My best guess is 4-6 torpedo hits, with two on carriers. This does not sink many ships, or even cripple any carriers, but it leaves Nagumo at dawn wondering what else he is risking hanging around with several damaged ships.
Sommerville also had four battleships roughly 250 nm from where he hoped to make the airstrike on the Japanese fleet. Hypothetically they could have raced north and 'maybe' caught a disorganized & damaged enemy before dawn on the 5th. A lot of hypotheticals and risks for both sides.
...the submarines HMS Trusty and HMS Truant in the right place at the right time lurking around the Malacca Strait to catch the Japanese fleet as they're returning from the raid...
Even if they just put a few more holes in the enemy & don't sink anything important this results in a lot of damage to repair impacts planning for the invasion at Port Morsby/Coral Sea battle, and may butterfly away the Midway operation, at least as we know it.
Of course the RN wet dream is to have a couple carriers sinking or in flames after the torpedo strike. Get the Albacores turned around and get another strike in six hours later at dawn, then the BB squadron arrives right at sunrise & runs down the survivors. Its a reach, but maybe Sommerville will have Spruances luck of 90 days later.