I've done a lot of skirmishes where time is a serious factor. For example: trying to 2 man a Ra'Ka skirmish in the amount of time they give you is pretty hard. At least for us. We've been able to 3 man it - but even then there wasn't a lot of room for error. And we are pretty well geared. Not amazingly geared but well enough.
Also, the time limits on a lot of those notorious monster fights in Adoulin are way too short. A lot of casual players (like me) would like to be able to work on our plasm reserves in our off-time but can't, because there just isn't enough time for me to solo them. And I miss the days when I could wander around soloing NMs for fun while waiting for my friends to get online as I used to do in abyssea when that place mattered.
In my opinion time limits are an uncreative way to add challenge to any fight and should only be implemented on a very limited occasion. To rely on them as your chief source of challenge is flawed game design IMHO. It's also an impediment to a smaller group of friends being able to get things done.