Enable custom field checkbox if change window is a weekday and between the hours of 8 am and 6 pm

[Pavan Chiti]

Below is our requirement.

Issue type is Change. We have 3 custom fields in Create screen. Start date(Date Time Picker), End Date(Date Time Picker) and Downtime(Checkbox). Change window(Time between Start Date and End Date custom fields) is a weekday and between the hours of 8 am and 6 pm. If so,  Downtime check box should be selected as soon as the dates in the same screen.

Can anyone help me with the Scriptrunner script to make this work.

Any help is appreciated.