Matlab single plot with code present already

Here is what I am looking for:
Currently I have data and code where the points are plotting using a date value on xaxis and it is time series plot. I am trying to build a code which:
1. Compares start and end (dates) if they are same then do whatever the code is currently doing
2. however, if they are different values then I would like to plot them with an extended line before the marker. The line would basically start from the start value and end at the end value on x axis having the corresponding marker value at the end date

So, with my current code I already have the markers for the end date on xaxis, all I need is the line extending those markers starting from the start date if the dates are different