Hello!  I am having similar challenges.  I used QBD and QBT.  We do not use jobs, just customers.  I initially had "everything" set up to "billable" - but I have an "admin client" that is nonbillable.  I changed for admin staff and all was working well for a while, but now I have a staff member whose time entry was requiring the billable field but it was grayed out.  In order to fix that, I've followed the above instructions - but now everything default's to "No" and I want to default to "Yes" (majority) with option to change to "No". 

I've gone around and around with reviewing settings and preferences in QBD,  preferences and custom fields in QBT, and can't seem to resolve.  Is there a way to make a particular customer (my admin client) default to billable NO and all other clients to billable YES?  Or a way to make YES the default for every entry?  I'm concerned my employees (or I myself) will miss the manual entry requirement and we'll be giving our time away.