Why is my Time Ruler in After Effects displaying seconds like this?
I know that Cmd clicking on the time stamp in the left corner alternates between frames and seconds:


Thats exactly whats happening here.You switched to frames so After Effects is showing the frame count instead of a second count. Do a Ctrl / Cmd click on the time stamp and you will get seconds:



To see all time values in the timeline simply drag the zoom slider to the right or use Alt and the mousewheel in order to 'zoom in':