Ride cut short - any benefit to finishing it in evening?

This isn’t the first time this has happened, but today my 30 mile planned training ride had to be cut short. I only got in 12 miles. Is there benefit to hitting the rest on the trainer tonight, or just write it off? I know some people believe in not worrying about a missed workout as long as you get in the long weekend run and swim.

I am MOP at best and this will be my first 70.3 at Oceanside so whenever I miss a workout I worry it could make it more difficult for me to complete the event.

Any insight is greatly appreciated.

Brian