My best guess is late autumn next year
One of the things about British politics at the moment is that there is little speculation about when Sunak will decide to go to the country. Normally in the fourth year after an election, you would expect that to be happening.
The Tory majority is large enough for Sunak not to be concerned and he will go when the time is right for his party and his chances. He’ll also want to stay at Number 10 as long as possible and he’ll be conscious of what happened to TMay at GE2017 when in her effort to increase the CON majority she ended up with no majority at all. This was in spite of having poll leads of 20%+
When Johnson was PM he changed the law to revert the decision as to the general election date to the PM himself so this is all in Sunak’s hands.
Unless there is a dramatic change in the polls my guess is that the election will be called in October next year to take place in November.
This would make an interesting betting market.