If go into the Points menu then Edit a point that was collected with that base station and then click View Data and then Base Point Position and use "Save as new point". A new Base Setup routine is currently being worked on that will allow the base point to be saved when the base is started. It will also simplify the process of starting the base.
When setting up my base station on a random point, I usually set it to burn for 30 minutes. In the new Rover/Base Setup It only has an "Autonomous" setting. How long doe this take and how accurate is this setting?
Typically autonomous positions are usually within 10' in open areas I believe. In Base/Rover Setup a single epoch is used so it is instantaneous. To get an accurate base station position you need to record the GNSS data and then later send it to OPUS or DPOS. Once you obtain the OPUS or DPOS position, you can update the base station position and correct all the survey points collected with the base station at that point.
With J-Field you can currently adjust the coordinate of the base and then recalculate the coordinates of all those points collected from that base coordinate.
To do this go to Points and choose a point surveyed from that Base position. Click the edit button and then the button containing the Antenna Height. It will then list the statistics for that point, click the Base button and then enter the adjusted position and click ok. You will be prompted if you want to correct all related surveyed points, choose yes and all your points will be updated using their vectors from the OPUS coordinate you entered.
Any calculated points or imported points in the database will NOT move with the change in base coordinates. This is reasonable since there is no connection between the base and a calculated point, but it should be understood and considered when using this technique.
Also, when changing the base coordinate, the default system you will be presented for the base coordinate will be WGS84/ITRF2008. You can change this to show any coordinate system in the library and then edit the coordinates.
For the time period, I let the base station record the data the entire time I have it set up and am using it as a base. Accuracy improves with time. The minimum time for OPUS Rapid-Static is 15 minutes.