This is what I figured aft looking at the trial run day...
Peak hrs:
HarbourFront - Promenade: 4 mins. Alternate train to MRB & DBG (8 mins)
Off peak hrs:
HarbourFront - Promenade: 4.5 mins. Alternate train to MRB & DBG (9 mins)
just in.
(from SMRT twitter)
No train service between Promenade and Marina Bay Circle Line stations due to track fault.
Train service between Dhoby Ghaut and HarbourFront Circle Line stations is normal.
UPDATE: Service has resumed between Promenade and Marina Bay Circle Line stations.