Sorry, but I must have misread your first question. I thought you asked if you could have a seperate waiting period for a particular expense that is covered under the health plan.
You can have a waiting period up to 90 days, and actually there can be some slightly more due to issues such as obtaining a certification/license for work. You can also have different waiting periods.
I don't understand the last part "Also, is a period tied to "particpation" in the plan as opposed to service itself really a waiting period? It is not based "solely" on the passage of time"