Every frame in GIF-animation can have his own delay (for example, one frame can freeze on 5 seconds, and next frame - half-second, as you wish). Select frame in list, press '5' and enter delay for him in ms (milliseconds - 1/1000 of second). Entered delays already will be 'rounded' by 10. And when you enter delay - you can select not 'Ok', you can select 'For all' - then entered delay will be writed to ALL frames in the list.