Copy and Paste Button Using JS With 0 as the Lead

I am needing a script so that I can create a COPY/PASTE button that will copy/paste multiple fields.

The field value will be time showing as a 5 digit (00:00), so there will be at times a 0 as the leading value in the field. 

I have search for an answer and was able to get the button to work, but not on the 0-lead fields. ie 08:00 would show as 800. (I don't know if it matters, but the user will enter 0800 and the field will change it to 08:00.) It seems to work perfectly with all the other fields. 

I have read to add valueAsString to the script, but obviously I have no idea what I'm doing. Here is what I am working with:

this.getfield("SunRow3").value = this.getfield("SunRow1").valueAsString;

Thank you in an advance for any assistance.