I have issues with JLH1964 tone and attitude but I don't think what he's requesting is unreasonable either.
When a product transitions to a SAAS model, this is one of the responsibilities you would expect them to acquire.
I work for a company that started as a small startup and grown into a widely used service and one of our biggest ordeals during that growth was building processes that would allow us to keep minimum downtime and providing prompt support when that downtime occurred. No matter what time of the week that is.
Now, I have no idea how much money Scirra is making with C3 so there may not be there yet but is definitely something that IMO they would need to start thinking about. I agree that JLH1964 should expect to be able to use the app as expected on 99% of the weekends. Reasoning that Construct "can't adapt to his schedule" is ridiculous.