I had been waiting for 30 minutes when the shop opened. vs I was waiting for 30 minutes when the shop opened.

Some examples from the web:

• I had been waiting for 4 years for my trip to be approved.
• This was the moment olive snook had been waiting for.
• Rory got the call that he had been waiting for.
• That was the everlasting moment he had been waiting for.
• After a grueling week of manual labor, the day Barry had been waiting for had arrived...
• It was as if he had been waiting for them.
• For Stroud, that microscope was the lantern he had been waiting for to light his way into the marvellous and exacting truth of scientific research.
• In the wake of this whole crazy circus, The call came in that Buck had been waiting for.
• Yes. Joanna Woodleigh, late stages of renal failure, had been waiting for two years.
• It was like the keys had been waiting for those notes.
• And I had been waiting my whole life for strangers to come up and ask me that question.
• I had been waiting so long... I was afraid she wouldn't come.
• However, the in-use stability has been demonstrated for 30 minutes when stored at 20oC - 25oC.
• Haman the Agagite found the opportunity he had been waiting for.
• In reality, however, that authorisation, which the ACP states had been waiting for for months, seems more like blackmail as far as they are concerned.
• The kind that looked like someone had been waiting for someone - soda can, candy wrappers, and an empty pouch of pipe tobacco.
• She kept me waiting for 30 minutes.
• But, there was still an "I love you" in there. I had been waiting for that.
• These people have been waiting for 30 years in the Saharan desert of deserts.
• That day, my father finally got to do something he had been waiting for since the day he got married... be right!

Some examples from the web:

• However, the in-use stability has been demonstrated for 30 minutes when stored at 20oC - 25oC.
• She kept me waiting for 30 minutes.
• At sunrise I was waiting for you.
• Some guy was waiting for me outside the shop.
• I was trying to tell this gentleman that I was waiting for somebody.
• I was waiting for a company.
• I was waiting for you to ask me that question.
• You know I was waiting for that moment.
• I was waiting for a tanning bed when...
• Yes, I was waiting for you.
• I was waiting for Ga Eul's boyfriend.
• Yes, I was waiting for you.
• Me too, I was waiting for you.
• I was waiting for somebody to fix things.
• I was waiting for you to come and get me.
• The one I was waiting for is at Nizaemon's.
• I was waiting for the rehearsal to end.
• I was waiting for you to bring Barry home.
• I was waiting for her to call again.
• Once I was waiting for Salladhor Saan here in Braavos.