Time can be broken up into segments, like Avalon Hill's phased turns which allowed for "simultaneous time" for both players. "Artificial time" is the basis of all game and simulation design even if it is as abstract as the "I go then you go" turns that most people seem to think is how all table top games worked. I have an even more sophisticated way of doing this, but the original basic Avalon Hill concept would work for you.
Each player could have a block of time to use. This might be a sophisticated phased turn system with a sequence of play, or as simple as having for example 60 "time points" to spend each "turn" taking actions. In this example a "turn" would obviously be 1 minute. In an RPG you might say a turn is one week, and each player gets 7 actions per turn. Players have to wait for all actions to be completed for all players before the next "turn" (ie set of actions) begins. This can be done in real time, in fact sophisticated enough "turns" are real-time running in slow motion.
There are as many ways as using this concept as you are able too imagine, there is no one way of "doing it right", but a real-time version of Avalon Hill's simultaneous action phased turns would allow you to do what you are wanting to do in a good way. It can be as simple or sophisticated as you want it too be.
