It is probably not too late to put holes in your trays if you need to. If you have seedlings you can work between them, use something long and sharp, like a skewer or one of those tools you use to make holes in wood before putting screws in, and just make one or two holes in the bottom. Or on the side but right at the bottom of the tray. I find that it is easy to keep the right moisture balance in seed trays if they are not outside so I don't bother with holes...