Which ISP? It's more likely an issue there, than anything in particular wrong with Mail. Are you using IMAP or POP? Does Mail check automatically for mail every few minutes? Do you get Mail on any other devices - iPhone/iPad etc. and if so, how has it been there?
Are the emails there in web mail but not showing up in Mail (i.e.: how do you know it's "late" - and is it late arriving in Mail or everywhere?)
More details, please!
BTW - if you post a header or two, with your email addy and the sender's obscured, we might be able to see where the email went and when.