Not possible at the moment, All spawned map items are set by a single value in the config.
However the best way to get around this if you want separate times on different spawned items is just to create them as a resource or event.
So have the resource image the item you want and the exhausted image as blank.
Set the respawn time to what you want
Set health of the resource as 1
Have the resource drop the item.
Another way is to do this via events (multiple ways) one way is (not tested, just off top of head as at work atm):
Have an event as a player touch
Give player Item X
Wait 60000ms (60secs)
Exit Event process
If you want the item to be obtained one per player, then add a player switch to trigger when the player receives item to toggle on/off.
The engine is very powerful in a sense that you can get around things using events / resources and such. Just need to explorer the engine more and see what is possible