Yes, you could put the plug plants in there, they'd be fine.
However, considering that the date is only 8 weeks away there won't be many plugs that will develop and look wonderful in just 8 weeks.
I think you might just have to go and invest in a load of pot grown plants from a nursery or garden centre because that's the way to have established plants in 8 weeks time.
It might have been a bit better if you'd planned the plant part of the event about a year ago with regards to having great displays for then.

The plants that will probably attract you, if you go to a nursery/garden centre etc. will be bedding plants because they'll be up, ready and flowering from the day you buy them to the actual day.

One particular plant springs to mind, which is coming into the Garden Centres now, and that's Erysimums. They're perennial wallflowers, and the best known one is 'Bowles' Mauve'. However, I have several different ones - Apricot Delight, Rysi Bronze, Rysi Gold, Constant Cheer, Winter Sorbet and several more. They're just coming into flower now, and they'll keep on flowering right through until the frosts.

Nearer the date, look for Verbascums and Polemoniums. They should also be in flower by May. They can be planted out as soon as you find them.

Senecio is another good bright plant. It isn't hardy, but it would look great in pots. You should be able to get Pelargoniums in flower by then, too, but watch out for late frosts - and pop them in the greenhouse if it's threatened.

Take Louise's advice and buy plants in bud or flower and 'dress' your garden for the event. As she said, plug plants are very unlikely to be in flower by then, I'm afraid.