Iirc b800k must show in your account as transferred in from abroad, be in 2 months before and 3 months after application, can only reduce to minimum b400k 3 months after application and must be back up to b800k 3 months before renewal. Anything outside this is why agents charge for IO to 'misread' dates, amounts etc.
Use an agent once, and irregularities will be seen at the next renewal, or if its checked by IO or others at any time and visa deemed to be cancelled.
If UK you cannot use the b6500 monthly pension route as UK government agencies will not provide the required certification.
The interest you 'lose' on b800k is hardly worth worrying about.
OP needs to check with the IO he uses (as it may vary)if it's 3 calender months or 90 days for the money to be seasoned. (Tbh I've only seen 90 days in 'presence' terms)
It's a small difference but may be vital.
Maybe IO will let him make up his own calender that has 31 days in April 😮
But as others have said train wreck of a question.