We could have one central NPC such as the Time Guardian or Mrs. Smith be in charge of timed missions (or this job can be given to all the shopkeepers throughout the Realms). The player would go to the mission leader and type Mission Request or say something like How can I help you? or whatever. (I prefer a key word like Mission so that a list of MISSION commands can be made. I will go into that in a bit.)
The mission leader then tells you about some baddie some place who has killed their dog or stole their favorite teddybear or whatever. The mission leader tells you the name of the NPC and the area and zone name the NPC can be found. The player would only be given a certain amount of time, such as 15-30 minutes depending on the mission.
To check how much time you have left, you could type Mission Time and you would get a message telling you what time you have left.
To get the info on your current mission, type Mission Info. You would then get the NPC name and area/zone, with any brief relevant info.
[Mrs. Smith tells you, 'You are looking for the CITY GUARD near the LONDON DOCKS located in VICTORIAN ENGLAND. Please hurry! You have 12 minutes left.']
To get directions to the area the baddie is located, type Mission Location. You would get a message telling you how to get to the area (not the exact room) that the baddie is located. Perhaps this will be a command available only to Newbies?
[Mrs. Smith tells you, 'To get to VICTORIAN ENGLAND from the Time Guardian, you will need to say FUTURE, go w 4n e n e. From there, find the entrance to VICTORIAN ENGLAND. Good luck!']
You go kill the baddie then type Mission Complete. Going back to the mission leader doesn't have to be necessary (unless, for coding reasons, the gold has to transfer from mob to mob/player.) If that was the right baddie within the right amount of time, you get some exp and some gold. If that wasn't the right baddie, you would get a message saying so. If you failed to complete the mission within the allotted time, you lose nothing but you have to wait a certain amount of time before going on a new mission.
The idea behind it is to encourage players to explore, and reward them for it. This is a great tool to get newbie out there, having fun, learning new things about 4D.