Currently there is no way to add a custom field that will display a time or duration.  Closest thing is a Number custom field which only takes integers or decimals.  We need something similar to the Original Estimate field as part of the Time Tracking feature.

Use Case:

Want to add a "Baseline Estimate" field that we would like to compare with the Time Tracking Original Estimate field that is already there.  If we could add this as a custom field then we could have the data and then run searches or reports as comparison.

Workaround:

None currently.  There are also no plugins available in the Cloud version that extend the custom field options.