If you're flying on a 61.75 FAA licence, issued on the basis of your EASA PPL, it will have the same restrictions as your EASA PPL. If your EASA PPL includes the privelage of being exercised at night, so will your 61.75 FAA PPL. If not, your 61.75 FAA PPL will have a restriction to day only.
(My present 61.75 allows night flying - I previously had one restricted to day.)
I doubt if the US school can do anything to alter that situation in a short time.