If you do meet him for coffee on Sunday, and it goes well enough for you to care, it would be reasonable to ask him what the possible hitch had been, and play it from there. If he's on call every third Sunday, that's something to plan around in one direction. Again, some things for an elderly or sick relative might fall into that category. On the other hand, if it was a just-for-fun social thing, maybe a friend who dithers about the date for a barbecue or whether he can get concert tickets, you can decide whether that's okay as him thinking that if they stood him up, he could meet you sooner, or if it's not okay because you don't want to be anyone's backup plan, even this early in getting to know him.
Text is hard to get tone across in, and I think brevity can make it worse. I do pretty well having real conversations in long-form online or smartphone chats, but wouldn't want to do anything much subtler than "My train is late. Meet at South Station or at your place?" in a 140-character text message.