The Inform 6 compiler seems to use this bit to signal that the statusline should show time, even in v5, and the I6 library reads the bit to check if it’s supposed to show time.
How safe is this? I imagine there could also be interpreters which set the bit to zero before the game starts.
A new system variable sys_statusline_flag is set to 1 initially if you have used the statusline time; directive in your program to show a clock, and to 0 otherwise. It can be changed by the program.
So this is exactly what I’m talking about. The Inform 6 compiler uses the header flag to communicate whether or not the game should show time on the statusline, even in a version 5 story file.