Help with title please

Can anyone help me with this? A time/dimension travel machine is constructed. A single-occupant capsule sits on a tower with rotating rings surrounding it. The capsule falls into water. The traveller has a rough ride through a wormhole.  No-one believes him as it takes only half a second in real time but the tape in the capsule runs for 18 hours. Driving me nuts trying to remember the name! Thanks for reading.