The bucket starts at 800, and is constantly refilling at a rate of 1 every 0.075s (so 800 per min) up to that maximum of 800.
If you use < 1 request every 0.075s your remaining will be ~799, as the bucket is refilling faster than you’re using it. If you make more than 1 request ever 0.075s the bucket will progressively empty (faster the more frequently you make requests) until it hits 0, at which point you’re effectively throttled to 1 request every 0.075s as any attempted beyond that will hit a 429 response.
If you burst beyond 1 request every 0.075s and the bucket starts to empty, it’ll progressively fill up again when you slow to less requests than that rate.