Sale of an Inherited Home - When counts as ownership

IANAL, but I think it would be when it was put in your name. Prior to that it was owned by your mother's estate, not you.

You might be able to convince the IRS that since you were the sole beneficiary, you effectively owned everything in the estate when she died. And maybe they won't argue over a 1 month difference (OTOH, how hard would it be for you to delay closing on the sale for a month?).

As pointed out in a comment, since you already moved to Florida, this point is moot. To claim the exclusion you have to own and live in the house for 2 years prior to the sale. So even if we use the date of death, you would have to keep living in the house until June.