I am fairly new to scripting, so I'm not sure if this would really work at all... Some help would be great!
Ahh, no. Not likely. The fQuestDelayTime variable is for setting the time between executions of your script. Setting it to 0 has no effect, it just reverts to its default of 5. And unless you are setting it to different values throughout your script, checking for its value is pointless.
First, I suggest you jump over to the Oblivion Mods forum and search for a thread entitled Immersive Thievery Request. That should cover setting the ownership of an item the player picks up.
As for setting a timer on the ownership reverting back to its original. I'd suggest a data structure to store the type of item the player has picked up, the number of items (say, if the player picks up a stack of arrows), it's original ownership, and the time it was picked up (I'd suggest in hours, if you're happy to round it to the nearest hour). In other words, an array of arrays (see OBSE docs http://obse.silverlock.org/obse_command_doc.html#Array_Variables, ar_append and ar_list at that link may be helpful too). Then, every hour you can check through your array for each item whose time has elapsed (if you store them in the order that they were collected by the player, you'll only need to iterate through the array up until the first item whose timer has not yet elapsed = better performance
).
Once you detect that an items timer has elapsed, you'll need to access the players inventory, once again, http://obse.silverlock.org/obse_command_doc.html#Inventory_Reference is your friend. Make sure you read this thoroughly. You'll need to be careful how you handle stacks of items, where only some of the stack includes items whose ownership you want to revert, and the rest of the stack should stay as the player ownership. GetInvRefsForItem to get those items. GetRefCount to get how many there are. As far as I'm aware there's no way to act on only some of the stack of items, so I'd suggest remove them all with RemoveMeIR. Then use CreateTempRef, SetRefCount to create 2 stacks of that item (with the right number in each obviously), one keeping the player ownership, the other with the original ownership stored in the above data structure. Then put both stacks into the players inventory with CopyIR. You'll also need to be careful here about items with different health and/or other properties.
Hopefully thats enough to get you started...
Edit: Actually, I should add that I haven't actually done this myself. I'm just going off the documentation... oops.