Just some more info. I did the trip last weekend
There's Transnasional Bus from Lavender and 5 Star runs a bus that leaves at 6:30am. The 5 Star bus is quite expensive, but an option if a night in Mersing is not an option.
A taxi from JB to Mersing is around 150 MYR.
Since we were four we took the taxi option. We met the taxi uncle at 7am in JB, had some breakfast on the way (bah kut teh in kota tinggi and some tosai and banana prata
) and comfortably were on the 11:30am ferry.
The round trip with the speed ferry is 70 MYR, travel time was roughly 1h 45m. No more speed boats due to an accident last year.
The best ferries are from BlueWater, tickets at Mersing Jetty counter 8.
We arrived in Tioman just in time for two nice afternoon dives.
Last ferry back is at 4:30pm on weekends and 3:00pm on weekdays.
I was diving with Tioman Reef Divers (Tekek, staying at Swiss Cottage or Babura Seaview) and would be happy to dive with them again.