I've done all the steps you said, and it isn't syncing from QBDT to QBT. I'm wondering about one statement you made:

To begin, make sure your desktop file is integrated with your QuickBooks Time account using the Web Connector feature. Once ready, create your custom fields in QBDT for class or service items. 

Is the problem because I am not syncing a class or service item? If, in QBT, I go to QBDT Integration Preferences, my new field does not show there. Shouldn't it?