I can't attend my classmate's daughter's wedding because of the rush of time. How to write short messages?

I'm very sorry that I can't come to your daughter's wedding. Here, I extend my most sincere apologies and best wishes. I wish your family harmony and your grandson an early date (write some greetings)! Come out for dinner sometime! You can make an appointment to get together. )

Basically: explain why you can't attend, offer blessings and be polite.