Okay so if he is the ONLY person than can offer this particular help and you can get that help in 15 mins.... I can't imagine him being the ONLY person that can help you or provide whatever service you need.

Maybe next time when you sit down ,ask specific question right then, remind him you only have 14 mins left, if he doesnt provide an answer then remind him you have X mins left and you need X help or you will find it elsewhere, get up and leave.

Im sorry I am blunt and If I am running as lean as you have to due to your financial obligations I would be blunt and either get what you need or find someone who will.

Id rather take my chances on finding my much needed help elsewhere than to listen to someone ramble and take my money and I still have no information or whatever it is you need from this person .

No one is the" know all be all" of anything .