Eight 4" by 5" inch solid rectangles into a 10" by 16" rectangle? Definitely not following. Did you want unfilled rectangles?
The limitation is on the height of whatever you are engraving. Engraving takes a long time to travel vertically, since the head movement for engraving is always left to right (horizontal).
So your ten inch tall group of rectangles will probably take twice as long as the five inch tall one IF you are engraving it.
If you can get by with a single line though (which is going to be pretty narrow) it will take a matter of seconds to Score it instead of engrave, because the machine will travel vertically as well as horizontally.
Gonna be a very thin mark though.
Edit…no that’s not right either. Widening the engraving path horizontally as well is going to up the time.
I’d go with 4 times longer. That and five bucks will get you a cup of coffee at any Starbucks.