A well planned expedition will be more enjoyable and safe experience with a bigger probability of success.
Assuming that a Northbound single-day traverse is contemplated, it makes sense to start very early from Pen Y Pass. The YHA hostel is perfectly situated for a pre dawn start and can be accessed via public transport. The Society is keen to see better public transport links but at the moment many Sherpa bus services tend to shut down soon after office hours.
After completing the three summits of the Snowdon group (estimate 3-4 hrs), you will walk down the Llanberis Pass to Nant Peris. This narrow road has no footpath or speed limit and is quite dangerous. There are no shop facilities in Nant Peris, and a support vehicle providing breakfast butties and tea would be very welcome at this point.
After leaving the road at Nant Peris the second group of summits, the Glyderau, are encountered. This section will start with Elidir Fawr and conclude with Tryfan. Most will opt to descend to the A5 down Western Gully. Having friends to meet and hand over food, drink and clothing changes would be particularly welcome at this stage before the Carneddau are contemplated.
It is several kilometres from the final summit of Foel Fras to the nearest roadhead. A long suffering supporter would drive around to Bwlch Y Ddeufean (no public transport) to collect some weary walkers as they descend from Drum.
Anyone without the luxury of a support crew or a pre placed vehicle would probabably opt to descend to the coast at Aber. You might be able to get a bus to Conwy from Aber.