No, not roaming. Was sitting at home when the 20-minute differential between delivery to my computer & delivery to my phone happened. And this has happened at various times of day, in various locations, and I've only noticed it over the past few weeks. I will begin to track what carrier the messages in question are coming from, in case the problem is that carrier and not GV. I can't see that it is my carrier or cell tower location since I have had the same carrier since last November.
Speaking of towers, I entered my address on Antenna Search (interesting!) and since I live in downtown Manhattan the results are dense! Maybe "network traffic" is the right answer ... Within a 1-mile radius:
Thanks, Papa Bear. I just hope this problem stops as mysteriously as it has started. If others are not currently complaining (and the threads I found re SMS delay were quite old, seeming to date back prior to push technology being introduced for GV SMS which used to rely on polling their server every 5 minutes or something like that) ... then I have to chalk it up to "something" on your list.