I don’t know if I understood your question correctly but if you want to repeat a certain action every “X” seconds you could use InvokeRepeating which is really easy to use:
function Start() {
// A unit will be produced every 60 seconds
// The "0" in the 2nd argument is the delay to start producing. So 0 seconds i.e. start producing now
InvokeRepeating("ProduceUnit", 0, 60);
}
function ProduceUnit() {
// Your unit instantiation code would be here...
}