sorry for the stupid question...

in other platforms, i can choose the interval to add vertical grid lines

e.g. in my 1 minute chart, i want a vertical grid line every 5 mins

how do i do this in TOS? i must be overlooking something ...

thank you in advance for your help!!

whats1thingnow 

how do i do this in TOS?

I think you're asking for more customization than ThinkOrSwim allows.

You can show grid lines. (see the appearance settings...)

These lines are drawn corresponding to the time axis labels. The lines and labels will change their interval, so that they'd always display with reasonable spacing between them, as your chart is zoomed in or out.