[whpalmer4]

Just make a finish-start dependency from the first task to the second. OmniPlan will automatically estimate the date the second task would be able to start, and will adjust it if the first changes.

In general, it's better to build your plan with dependencies rather than plugging in dates. If you build the plan with Tom doing one task on Monday (for 3 days) and starting another on Thursday (for 2 days), you get the same appearance on the Gantt chart as if you assign Tom a 3 day task on Monday with a finish-start dependency to another task (for 2 days), but only the one done with dependencies works well if Tom's tasks don't work out exactly as estimated (in my experience, that's almost always the case!)