If this type of work has been done previous, you could reference that ticket for a general guideline on how long that item took. Otherwise think about how long

If this type of work has been done previous, you could reference that ticket for a general guideline on how long that item took. Otherwise think about how long it would take you to accomplish given your knowledge and experience then account for the developers knowledge and experience, and pad the time a little bit, also account for other departments involved. A lot of times we build part of the task for a quick estimate of how long that took (nothing more than an hour). Also if there are any examples or existing proof of concepts that can be used to accelerate the dev time. And lastly remember that its only an estimate.