Getting there: Arrive by ferry at 0645. Ride to Caen (17km).
It's a slow 17k (assuming you use the canal path - recommended, it's direct and paved, but shared use of course), and the last bit (approaching the station) is fiddly. I would expect at least 1h15 from the border control to the station. The night ferry often docks early but getting through the border is a huge unknown unknown at the best of times, usually quick enough on a bike but well worth being at the front of the queue to roll off the ferry.
The station itself is not very bike-friendly - you may get less than 10 minutes' notice of which island platform the train will depart from, then you have to negotiate small crowded elevators down to the underpass and back up at the right platform all in that short time. Last time I was there one lift we needed was out of service and of course bikes not permitted on escalators.
Getting back I'm not a blagger by nature but I must say I've never had any trouble just turning up and getting on the next ferry, with a bike, at Ouistreham.