Hi,
there is a Holidays/ Working days calendar (IMG -> SAP NetWeaver -> SAP NetWeaver -> SAP NetWeaver), which you can later assign per currency (IMG -> Financial Supply Chain Management -> Treasury and Risk Management -> Transaction Manager -> General Settings -> Transaction Management -> Currencies -> Assign Calendar), so system is checking against it and is providing warnings if some dates in your deal are falling on a holiday or a weekend; you have an option to ignore this warning, of course it it makes sense.
hope this will help you.
Kind regards,
Renatas