There are three scenarios where the time limit comes into play.

The first is when the aliens are owning the marines but cant manage to kill the chair. This situation is extreamly frustrating for the marines and in these situations the shorter the time limit the better.

The second is when the aliens and marines are equally matched and in a stalemate. I have observed on other servers with longer round times that during these stalemates marines camp their base until they get more powerful and then end up pushing the aliens back to the hive for a win.

The third is when the mariens are overtaking the aliens in the last minutes and just as the time runs out the hive is killed or very close to death. I dont see a problem with this. The aliens were able to hold off the marines and deserve the win. This situation may be where most people have a problem with the time limit.

People have problems with the time limit for various reasons, and if one sticks out as a substantial majority then maybe some tweaks should be done.

As far as filling the server goes, If people are sticking around because they like the long combat games they may not be the best people to play NS with, or they may leave once the map switches to NS. Unfortunately the TG server is not popular enough to play NS maps all the time, I think most regulars have jobs or school to attend to during the day... so just be patient and join the server in the evening when a number of regulars are around. While waiting try playing NS or CO elsewhere, if you dont expect a good game its not so bad.