After a restart for what I thought was an unrelated issue, when I tried to launch SD I got the same message (although this time it said 3 days).
The first time it came up I clicked Check for updates and SD hung and I had to force quit. After that, again, the mac was in an unstable state (couldn’t type in documents, sometimes no response to clicking in the dock or menus). I shutdown the mac and started again.
Launching SD, this time I hit Continue when the update alert came up and again SD hung. Before force quitting I took a sample and saved it, but I couldn’t type anything in the save dialog. Looks like my mac may again be unstable.
(FWIW, the reason I was launching SD was that a droplet I’ve been using now returns an error that it’s not allowed access to control Finder. Checking preferences it clearly is. The applet was recently moved into another folder and back to its original if that makes a difference. I was going to edit it in SD and see if that fixed it. I’ll give up on SD for a while and try SE instead).