Construct2 when going to a layout will always start it like it's never been played unless you tell it otherwise.
For some games it will be enough to have changed global variables for it to resume where left of, but for more complicated games the state of the layout should be saved and retrieved on resume.
If your only issue is the time variable, probably you have an event on start of layout that changes it, so you should add a condition to the on start of layout to not reset it if coming back from the main menu.
You could do this by adding a global variable called resume and set it to 1 when going to the main menu and on start of layout check if it's set to 1, or just check if the global variable time has changed and if so don't reset it.