Yes, there is. But just remember, if you are arriving in your own car, under no circumstances attempt the walk over the lava field on your own. Wait for the guide and the rest of the group, who will be arriving by bus.
The tours start at 08:00, 10:00, 12:00 and 14:00 from the central bus station in Reykjavik. The bus will arrive at the Blue Mountains cabin around 30 minutes later. If you are coming in your own car, you should be there at that time, i.e. approximately 20–25 minutes past the hour, at the latest. The walk will then start at around 30 minutes past the hour, for example 08:30, 10:30, etc.