I have never had an extended stopover but this is what I have in my T&Cs.
Not sure if they have changed as it isn't something I have looked into previously, but I have highlighted the section I believe is relevant.
I am not sure if there is an arguable difference between being "on route to" or "on return from".

4. Gold Guest List Redemption Reward

4.1. A Member shall be eligible for two Gold Guest List Redemption Rewards per Tier Point Collection Year starting on the date that the Member received an invitation to the Gold Guest List and was able to receive the Services. This does not affect Members ability to spend Avios in the usual way under the Executive Club membership Terms and Conditions.

4.2. The Gold Guest List Redemption Rewards shall be subject to flight capacity and availability.

4.3. All passengers must travel on the same booking as the Member.

4.4. Gold Guest List Redemption Rewards must be used before the end of the Tier Point Collection Year in which the benefit was issued. No Gold Guest List Redemption Rewards may be carried over and any unused Gold Guest List Redemption Rewards will be lost if Membership of the Gold Guest List for whatever reason terminates. There is no cash alternative or compensation available if the Member fails to use his/her Gold Guest List Redemption Rewards.

4.5. A Member can use their Gold Guest List Redemption Reward to book one one-way or one return trip, this can include a connecting flight to your onward destination for example Delhi-London-New York-London-Delhi. Stop overs on route to final destination are limited to 14 days. Side trips are not permitted, for example a trip that is not on route to your final destination, for example Delhi-London-New York-London-Rome-London-Delhi, the London-Rome-London would be classed as a side trip. Once the Member has returned to their original point of origin this is classed as one return trip.