However, a voucher later or even a destination airport food coupon upon arrival isn't a substitute for a real FC meal on a 6 pm departure.

My most recent experience with this was a TPAC delayed by about six hours, from a late morning to a late afternoon departure. FAs served the main meal "dinner" at the usual time relative to wheels up and the midflight and prearrival meals were also exactly as usual. In this case, there was an aircraft swap that was announced to be delayed as we waited for catering to be swapped, although amenity kits, menus, etc. weren't transferred to the new aircraft (but there were enough wrapped pillows and blankets, so the lesson learned is that if you deboard, think about taking the small items with you.