you can actually use the slicer to print more htan one thing at a time.

so 100mm by 50mm - and it's taking 5 hours !
What speed and layer height are you using ?
That's ridiculous - even for an ender 3 - I mean I know they are slow - but damn, that's positively glacial !

But basically the slicer will not only generate duplicates for you, it will also lay them out on the bed.
Are you using cura or prusa slicer ?
prusa slicer is better :-)