Hi Strokey and welcome to the Hot Rodders forum.
That happened to me on my last 2 engines. As you found out, if all is well, it only takes maybe 30 seconds or so to get a good prime.
I primed a few minutes, turned the engine some, primed some more.
A word of caution. If you coated the cam real good with the cam paste, don't over prime the engine, you could rinse off all the paste.
Just make sure it fires quickly and runs for the 30 minutes at fast idle, around 1,600 to 2,000 rpm. Might be good to fire it outside incase you need to cool the radiator with the hose or something. Also, have a timing light hooked up and ready too so you don't have to shut it down for adjustments.