The best time to climb Snowdon is in the morning preferably as close to sunrise as possible. This gives you the best chance of parking if you are driving there as the car parks get extremely busy. Also the earlier you go up the earlier you will get back down and hopefully in daylight.
Many inexperienced walkers get into trouble in the hills because they fail to take into account when it will get dark. It is much different navigating in the dark compared to daylight. You should take a good quality torch and spare batteries as described in the What will I need? Section.
The time of year will make a big difference to your experience climbing Snowdon. During the winter there can be snow on the mountain and if this is the case specialist equipment and training is needed to go up. Even relatively simple routes can become treacherous when there is snow on the ground.
The Spring, Summer and early autumn are the best times to climb Snowdon as the days are long and snow is unlikely. You should always check the weather before you set off and make sure you are properly prepared for any eventuality.
It is important to remember that Snowdon is a mountain and the weather in the car park before you start and the weather at the top 3-4 hours later can be totally different. The two pictures on this page were taken on the same day.