How can I put an automatic date-stamp field in the form, that acts as a conditional field?

I see from the other thread where you commented that my colleague's solution worked for you. There is also an alternative way to set a date as current. Simply follow the steps below: 

1. Click the gear icon on the date field.

2. From the Datetime properties, select the Options tab then set the Default Date to Current.

Feel free to contact us again if you need further assistance.
Cheers.