18 month old hornbeam hedge pruning ideas?

I've just looked at my Hornbeam hedge and thought oops perhaps I should have lopped a bit off the top before now.
Its 18 months old and the chap who planted it told me not to cut it until it was established and now I just looked at a site saying I should have cut it down by a third when it was planted! Thats long gone now.
Spring has turned to summer with a big bang this year its 28 degrees today and I think I have missed the spring trim?
Some plants look bushy while others a bit leggy is it too late to give it a good chop? Any advice out there please. Many thanks Olive

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