There's a cron task that comes with Maximo, but isn't enabled. It will run the forecasts for all of the active PMs at whatever interval you choose. Actually, there are two cron tasks - one to run the forecasts, and the other to run the forecasts costs, if your Job Plans have Labor, services and materials on them.
If your PMs have floating schedules, i.e. the "Use Target Start Date" flag is off, then you also probably want to tell Maximo to re-forecast automatically when the work order is completed. That option is available in the Organization screen.