Good that there are still people who, like me, love challanges and do dungeons not only for drops/ rewards but mostly for the thrill and a feeling of accomplishment;)
All dungeons are doable at minimum req. level. I myself don’t quest after lv 35- i level up only on dungeons. Think of WvWvW as a mode for levels 80 which you can join faster (at any level) if you wish so.
I’ve finished every path in every dungeon with minimal required level. I’ve never kicked anyone from group who had level appropriate for the dungeon. Is it harder than taking level 80s with full exotics?- sure it is, but the dungeons are not so hard that it’s necessary to do it.
On the side note: I had few runs with lower level characters which went easier than full 80s squads- the reason: the knowledge and skill beats gear and stats in this game.
I didn’t like skipping at first but I got used to it. The thing is that you usually need experienced team to skip parts of dungeon or else it gets a lot longer than killing mobs- waiting for 1 or 2 people who couldn’t make it or trying to res them and wipe’ing. The good speedrun takes skill and knowledge.
The correct answer is: depends on the group. With good, experienced team the times given by AusterlitZ are about right. My 1st runs took me (and my casual guild) 3-5h for each path.