Similar meaning, more formal:
* Enjoyment: "While you were out having enjoyment, I finished the project." (Implies a more deliberate and conscious experience of pleasure)
* A good time: "While you were out having a good time, I finished the project." (Classic, casual phrase, emphasizes the positive experience)
* A blast: "While you were out having a blast, I finished the project." (Informal, implies a really good time)
More specific, depending on the context:
* Adventures: "While you were out having adventures, I finished the project." (If they were doing exciting things)
* A laugh: "While you were out having a laugh, I finished the project." (If they were socializing and being silly)
* A romantic evening: "While you were out having a romantic evening, I finished the project." (If they were on a date)
Adding nuance:
* A relaxing time: "While you were out having a relaxing time, I finished the project." (If they were unwinding)
* Some excitement: "While you were out having some excitement, I finished the project." (If they were doing something unusual or thrilling)
The best word will depend on what you want to emphasize and the overall tone of the sentence.