You should have started to fill in your gantt chart during your last sub-system. Continue to fill in your chart for this sub-system. Doing this should help you plan how much time you will spend on this sub-system of your project. Also, amend your gantt chart to show how your last sub-system ACTUALLY went (it may have taken longer or shorter time that you planned).

Put a screen print of your gantt chart into your project to show your progress and planning so far.