As folks have noted above, it’s not really the intent of what little Disney puts in writing. The one “challenge” is Disney’s inconsistent (or in some cases nonexistent) enforcement and at times inconsistent information given to guests. 5 people will post they were told 3 hours and 5 more will post they were told they can stay all day. So, the conversation does often devolve into “what’s right or wrong” or “I was told XYZ so that’s Disney’s policy” and people usually have strong opinions. Plus exact procedures can change on any given day based on the CM, resort events, etc.
Personally I take Disney’s basic statement as their rule and once done eating one should move their vehicle. Is anyone typically monitoring/enforcing this? No, not really. Could they under tight conditions? Possible. If 100 people did it each party night would it create parking issues for legitimate paying guests and others using resort amenities? Yes. GF’s lots aren't all that big (the valet lot there is too big IMO, but that’s a separate topic)…. Throw in a full resort, a convention, a big wedding, or whatever, that’s why most will say moving on is the spirit of Disney’s policy. I usually stay at places like the monorail or Epcot resorts, parking at some of them can be pretty tight in the evenings.
To answer your question about valet, yes, you can park all day if you pay valet (you can even move resorts if you’d like - just take your receipt, you only pay once per day).
Hope that helps. Enjoy your party night.