We don't really recommend worrying too much about how much money a client will have at a certain point in time - just whether or not they will reach their goals. That being said, clients often want to know how much they will have at retirement, or other points in time, and you probably would like to be able to answer their question.
This is actually pretty easy to answer. Just make a copy of the appropriate plan, and then delete everything after the point that the client is interested in. If they have elements that extend beyond that date, say rental income or a charitable giving goal, you will need to replace them with a scenario element that ends at the appropriate date. Now just run the plan and look at the cumulative wealth.
Remember that Monte Carlo analysis gives you a range of outcomes, and not an impossibly precise single number. The 90th and 10th percentile numbers are there for a reason. Monte Carlo analysis is a club, not a scalpel.