In the past, I needed to add a date sequentially on insert of a repeating table.

I found a post by S.Y.M Wong-A-Ton that helped me achieve this.  Here is a link to that post: http://www.bizsupportonline.net/infopath2007/automatically-populate-repeating-table-infopath-sequential-dates.htm

If you are working on anything InfoPath, this site is a GREAT resource.  I highly suggest that you check it out.

I have included a sample form for you to download.  You can add this control to any of your existing forms.  Here are the steps for re-creating this from scratch

1. Add a group
2. Add a repeating group
3. Add two fields:  date picker and text fieldField 1 (date picker control)
   Field 2 (text control)
4. Right click on field2 and insert the following statement in the value box
   preceding-sibling::group2[1]/field1

Make sure to change the field names if different than the ones in your form.

Here is the form you can download by clicking.  AddSequentialDates