The pre-hopped extract doesn't need boiling like regular hops, since the bittering acids are already isomerized and are soluble in the extract. So if you were boiling for 30 minutes to get more bitterness, then you don't need to.
EDIT: If you're mashing with a lot of pilsner malt, then a longer boil is beneficial to drive off SMS, which later becomes DMS - creamed corn flavor. But you also want a longer boil to help hit your target OG (unless you compensate with not sparging and using a lot more grain) and also to get a good hot break + later cold break to reduce chill haze.
30 minutes with the extract in the boil sounds about right, since boiling extract hard is not good for the flavor. Alternatively, you can leave the extract out of the boil for the first 30-45 minutes and do a full hour boil, but whether you need that depends upon how much grain you have. If it's just a couple of pounds of grain, then 30 mins will be fine. More than that, and you may want to boil for longer.