Ideal Exposure Time and ASI1600mm

I’ve searched and read all the posts on this topic but am still getting only 0.00 seconds as an output from the Ideal Exposure Time (direct from camera images).

Using this camera specific info:

and my gain setting of 200 I have filled in:

2x2 gain: 200
Camera Gain (e-/ADU): 2x2: 0.5
Readout noise 1.5

I have not filled in any values for other binning as 2x2 is the only binning I’m currently using.

Am I doing something wrong?