72 hr visa before using our 1-entry visa

Myself and 3 other grad students will be traveling to Beijing for medical rotations for 1 month. While we will have entry permit for that stay, it is a one entry. We were hoping to fly into Beijing, give our home stay students our luggage, and then exit to Thailand for a short 1 week vacation before coming back to Beijing for our rotations. However, on that initial entry we would want to use the 72-hr free travel without our 1-entry one being stamped yet. Is this possible or will our 1 entry-visa be stamped and we will be unable to leave China at that time?