Yes, you can. If the dates of your work change from what was originally entered in Dial Before You Dig, scroll down to the Schedule section of the Details page and enter the new Requested Start Date / Requested End Date in the fields provided. Click Save Requested Dates to submit the amended time frame:
The requested dates will be forwarded to the road authority for their approval. If there are any scheduling clashes or other reasons why they cannot accept the new dates, they will counter back with their own proposed dates. If this happens, you can either choose to accept their dates (if they're workable) or counter back with another set of your own. This can continue until the dates are decided on.
If you have any questions about the time frame you'd like to choose, this can be discussed with the road authority via the Messages section, or by calling them using the contact details from your job confirmation sheet.