How long for renegotiated mortgage to be processed at the mo?

[Goldrill]

Just that really! We think our buyers may be considering asking for renegotiation. I know what to look for on the money but if it takes a long time we'll lose the house we're buying. Buyer seems to think a week tops. EA suggesting 26 working days in the current situation .... slight difference in expectations! Anyone had to do it lately?