My husband and I took our 14yr old grand daughter there on this past Thursday. We booked reservations online, and yes you can book glass blowing appts online after 3pm. Spots do fill up fast, but paying online made the whole process easier. When we went to the visitor center, we saw there were still several open slots for the same day. They have a computerized display board that is in real time with the slots available each type of glass making for each appt time available. I hope this helped answer your question. Check out the website ahead of time and look over the FAQ's it is easy to use and very informative. Have a blast with glass!
3 pm would be cutting it close I think. Depending on all the demonstrations and activities you all want to participate in. The other thing is the schedule changes for the activities and demo. I would suggest calling and maybe even booking ahead.
I'm not sure if visitors engage in blowing glass. However they have wonderful demonstrations with audience participation in the glass blowing event, glass breaking, a history of glass manufacturing and other visual presentations of the science of glass making. It takes a minimum of a half day to complete a visit so arriving at 3PM limits what you see and do.
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