[saluki]

Since you're new you might be able to get the time they have in mind by asking 'what are your expectations for this'. (keep in mind some managers aren't good at estimating development time or might try to low ball the time to see how productive you can be)

Other than that every task/spec is different. I would review the task/spec then get back with them with an estimated range of time. 4 to 6 hours/4 to 6 days and tell them you'll update them on your progress as it's completed.

Once you're working on if things are going faster complete it/test it/review the spec/double check it and then present it as things went better than my estimate.

If things are taking longer, go to them early with what is completed and an outline of items that are taking longer than your estimate and have a new estimate ready for the time to overcome these challenges and complete it.

I would say relax, be a good listener and communicator, re-read specs/requirements and make sure you're complete/thorough in your work keep them informed and you should do fine.

Since you're new try to find someone you can trust, to be your mentor, show you the ropes, help you out, bounce ideas off of, give you the lay of the office/land.