Well, first of all the Timer widget doesn’t have the ability to set the start and end time programmatically.
The Time Input widget does, but This isn’t done by a Set Property command, it’s done via a VirtualWrite command with multiple elements.
The widget properties that can be changed via Set Property are documented here:
I’ve not tried to update the start time and end time of the time input widget using an API call, but the syntax for multiple API parameters is update/V3?value=255&value=255&value=255
Also, the API calls are still affected by the GeoDNS issue, so it’s always best to explicitly specify the IP address of the Blynk cloud server where your project lives (obtained by pinging blynk-cloud.com) rather than using blynk-cloud.com and hoping that the DNS resolution works as expected.