Good morning
I would like, after sending the email, for it to display the message “Please wait in the airlock” so that people have the time to read it and then for it to automatically return to the screen1 screen where there is the menu.
I tried with a clock with a stopwatch but I can't do it. Would it be possible to help me?
THANKS
Add the block to navigate to another screen under when clock timer block with the block to stop the clock too 
I tried like this but it doesn't work, it doesn't stay displayed long enough before moving to the other page, I don't see what I'm doing wrong?
No , here is the click of the button, I think.
You have to add the event block of the clock, the light brown one , inside you have to add clock stop and navigate to screen .
So when clock tic you will stop the clock and open another screen
and additionally you should switch screens correctly...
see also App Inventor Tutorials and Examples: Manager Screen | Pura Vida Apps
Taifun
Thank you Taifun
Or try virtual screens 
Perfect, thank you very much for your help
