How to extend job duration (possible?)

[wdeveoper03]

Is there a way to extend job duration either by a day or two when as the job progresses both the buyer and seller realizes that more time is needed to complete the job perhaps a particular feature?
And in this case the seller is willing to work to get it completed as it may be his first gig and is not asking the buyer for more tip while the seller have the option of paying more or not adding more?

This is just to prevent late deliveries when the system does not know that deadline has been extended by a day or two.Thanks.