Well, you can get by with 60 mins if your boil is vigorous (especially the last half). You could bump it up to 90 mins without problem I suspect; maybe a tiny bit of darkening may result, but I doubt it'd be noticeable. Just make sure you account for the extra boil-off time with your pre-boil volume.
And yes, if you boil for 90 mins you just don't add hops for the first 30. Unless you're first wort hopping (not in this recipe).