Unfortunately, it won't work. This weedkiller is not a pre emergent; the active ingredient is glyphosate, and that's a herbicide that kills 'through the green', in other words, the weeds need to be actively growing when you apply it. This means, obviously, you will now need to wait a few weeks to see what grows and then apply the weedkiller. Its a pity you didn't ask for advice before you started, because the best way to approach the problem would have been to remove the existing turf, then dig the area over by hand, removing the roots of perennial weeds at the same time. Your problem now is that the Rotavator you used will likely have chopped up weed roots (as well as not getting deep enough for some roots), and depending which weeds were present, may mean you'll have twice as much weed regrowth as you had in the first place.

There are no pre emergent weedkillers for home use available in the uk, so I can only apologise for being the bearer of bad tidings. There's nothing you can do now but wait for growth.

Regarding residual effect in the soil affecting your new turf, in theory, glyphosate is rendered inactive once in contact with soil. In practice, in some soils, glyphosate is retained for a while. Note that this product, together with glyphosate products generally, is likely to be withdrawn from sale shortly because there's some evidence it's carcinogenic to humans, although it seems agricultural use will continue (thus ensuring we'll all still be eating trace amounts of the stuff every time we eat porridge or a slice of bread!)

The best way to make sure you have a weed free new lawn now is simply to wait until Autumn (sorry about that) and remove all the weeds by hand as they appear.
Autumn or April are the best times to make new lawns anyway.If you had couch grass or dandelions for example in the old lawn when you rotavated it you'll find they keep reappearing for a long time. I certainly wouldn't apply any more glyphosate as you have already used the professional strength which was unnecessary and as Bamboo says of no use once the grass and weeds have been removed already..

If you still have some of the weedkiller left take care not to apply it near any crops you intend to eat.

If you are going to turf rather than sow seed make sure you get good quality turf as some does have weeds in when you get it.

I'm not sure the weedkiller's been used already, steragram

Oh no. well that's good then.