Asking a journal for extended payment period
Usually there is a payment window of 30 or 60 days for example, so if it arrives  mid-August then paying in September is not an issue. Journals have dealt with university accounts departments before.

If you are the one stressed as you have to have it published to complete then you may need to be patient, but the payment itself should not be an issue.

For one paper, it took 4 months for the journal to get paid - several polite communications (and they were nice and helpful on both sides...) but all got sorted.