First off, as suggested in previous posts, we should be referring to these types of quests as evolving quests rather than timed. No quest in TES should be "uncompletable" (not a real word, I know) unless you as a player choose to outright decline it at the start or back out at a later time. I recall several quests in OB where you had the option to complete the quest in different ways, like Fingers of The Mountain. I'm not putting a spoiler on here in the off-chance someone has not played OB yet, but here are the details for those who have played already and want a refresher, http://www.uesp.net/wiki/Oblivion:Chorrol_Recommendation. Needless to say there are a couple different ways to complete this quest and even after completing, there is still a chance for you to do something else to cause a different outcome. In a sense, this quest evolved depending on how you chose to complete it.
This touches on what Res.Knight is trying to suggest, where a quest line changes/adapts as you go along, either due to the passing of time, or choices you've made, conversation paths or possibly other quests you've decided to complete first. Also, not all quests need to behave this way. It would just add some variety to the game if even a few were like this. You accept a quest...it may change over time, it may not. Since the quest shows no indication of whether it is going to evolve or not, you don't feel pressured to pursue it immediately, but you still could complete it right away, that's your choice. Now, say a few weeks or even months of game time pass. You go to get to your quest, and you get to the quest point, and what's this...
"I'm sorry, but the local Thieves Guild had to relocate because the city guard was tipped off about their location. We could have dealt with the guardsman in charge of the investigation but all of our members were out performing other jobs. Wait, were you thinking of joining the Thieves Guild? You were?! Oh, if only you'd have gotten here sooner, you could have helped us lead the guards on a false trail. Well, nothing to be done about it now. Would you like me to mark the new location of the Thieves Guild hideout on your Map? Okay, here you go. Be careful though, there are guards patrolling the entrance waiting to arrest anyone entering our new safehouse. You'll have to figure out a way to sneak past them so you don't get arrested."
So because you found out the initial location of the Thieves Guild, but chose to wait a while before going to that location, something happened; something changed. You haven't failed that quest, it just adapted to something in the city that happened over time. Had you decided to go there sooner, you might have had the same quest given to you, but this time it would be that someone tipped off the guards, and you would be given the option to lead them on a false trail, or you could go do another quest or some exploring and let the guards find the original hideout, and then maybe you'd be involved in finding a suitable relocation spot, if you didn't get arrested in the raid. Maybe you need to ask around to find a side or secret entrance if your sneak skill is not high enough to sneak past the guards to get to the main entrance. You can still complete this quest in some way, it's just that it got a bit more difficult after a long passage of time. Also, you wouldn't have even known that this quest evolved because based on when you came into the picture, it would appear to you as though Bethesda just programmed a static quest with a bit of a twist on finding this town's Thieves Guild. Any options you would have had by taking this quest earlier would never show up for you on the current playthrough so you would never know that you missed out on anything. But, on the next playthrough, you might find that this particular quest is somewhat different than you remembered and you'll think, hey, that's kinda cool.
Regardless of your actions, that raid was going to happen in this town at a specific time whether you were directly involved or not. Just because you're not there when it happens, doesn't mean that you will be unaffected by the outcome of that raid and its effects on the thieves of that town.
Apologies for a long post, but it seems like some people are getting a right bit peeved at this suggestion and I thought that maybe it could use some more clarification.
Cheers!