Even with a long transit time and, in some cases, flying non-RJ metal, I've been able to access the lounge. These have been my experience the last three times:

- was travelling with RJ operated/sold ticket and had a 6hour layover (entered at 11pm with flight the next day at 5am). They scanned my boarding pass and let me through with no issues.
- was travelling on a RJ sold ticket but the next flight was QR operated. The transit was 11hrs and overnight (entered at 01:00). The receptionist was a little hesitant at first, saying because it was not a RJ plane (my boarding pass was printed on a QR boarding pass), he could only let me in 3hours before. However, whether it be my charm or he just felt pity - he was kind enough to let me through.
-was travelling on a RJ ticket with an RJ flight. The transit was 11hours and overnight (entered at 23:00). Again, the receptionist was a little hesitant at first, but this time explaining the issue was because my flight was leaving the next day and hence he would not be able to let me in. However, he called someone and then said he can let me through based on me having oneworld sapphire/BA sliver status.

All times I went it was late night and the lounge was more or less empty. I think if it was busier, they may have stuck to the policy.