Do mortgage overpayments immediately reduce daily interest amounts?

Hiya,

Yesterday I overpaid my Nationwide SVR mortgage by 17k. I'm not on SVR by choice btw. I missed the deadline to switch my product before it expired on 1 February (I didn't know there was one!).

I was expecting my mortgage balance today to show as the previous balance - 17k, and therefore my daily accrued interest being applied to the new figure.

It hasn't, I assume because it takes some time to log on the system, but I'm wondering if the accrued interest will be revised?

If not, it seems a bit unfair that I overpaid but the daily interest didn't take it into account.