Hopefully your router is a plunge router, it can be done with a fixed base router but it's a lot simpler (and a tad safer) with a plunger.
(edit) You'll also need to figure a way to control the cutout as you finish the cut, ie. keeping everything from falling through the hole you just made.
If you cut it on a flat surface, remember that the router bit will cut into that surface. If you cut the hole after your table is complete tack, clamp, screw or whatever a couple of scraps to support the cutout.
I have access to an old fixed B & D router but are looking at purchasing a router for
this job and for other projects around the house. A plunge router would be way easier
of tackling this job.
Thanks for the idea of tacking the cutout . Nothing more fustrating than spending time cutting a board or an opening like this and have it destroyed and broken into
pieces making it useless.
Thanks as well to everyone else that has replied and responded so quickly !
Any other input anyone has will also be considered