Overlay clock switching automatically

can anyone explain about the "timer in WLED. maybe can point out a site that discuss or tutorial about it. Recently I made seven segment based on wled and enable to show it alternately using button. Right now I want to show it periodetly in certain time with single click button. I’ve try use “millis()” function like in usermod example, but I didn’t work. It also didn’t work too when using flag or boolean.

And how to enable correctly usermod “RTC”? already followed instruction and check the wiring but it didn’t work too.

Any help really appreciated.