In other words, does traveling time counts as working hours?
Generally no, because most employees only travel between home and the workplace and that's never been considered working time, even if you're suddenly required to travel to a different location with a longer commute.
However, the standard definition of Travel Time in the FLSA does consider travel time to be working time if the travel takes place after starting work and you're travelling between work sites. If there's a daily meeting at location A to start the day and people then move to location B to work, that travel time is work time. If you have to pick up gear at the main office before starting work at another site then that travel time is also work time and your employer can't require you to only clock in when you get to that site.
The big problem for your specific scenario is whether the act of coming together at the office before travelling to the job site constitutes actual work or not. Since you are required to be there at a specific time that supports the argument that this is the start of your work day and arranging of transport or even a simple greeting is part of that day's work activities, making any travel time after that working time. But make no mistake: this is a legal gray area.
Of course, a simple way for your management to get around paying you is to just require you to be at the conference site on time. Since you're presumably all functioning adults this is what they should be doing anyway, unless they're organising transport to help people out.
Keep in mind that no matter how right you are, making a big deal out of a few hours over an entire year is likely not a hill worth dying on and could be a Career Limiting Move.
The full section on travel time from the FLSA:
There are some "grey areas" about when the FLSA requires travel time to be treated as working time. However, as a general rule, "home to work" and "work to home" travel time is not work time, and this is true even if the "commute" is longer than normal, to or from a different work site than normal, or the employee uses a company vehicle for the trips. This assumes that the employee is performing no other work activities while commuting. Time spent by an employee writing a report is work time, even if it happens to occur while the employee is riding on a bus (or airplane) to or from work. Travel time which is "all in a day's work" is work time. Usually, this means that travel time is work time if it occurs between when the employee first arrives at the first work site and before the employee leaves the last work site at the end of the work day. The first work site is the place where the employee first performs work activities. For example, an employee who travels to the office, picks up equipment, then goes to a work site to perform the day's activities is working from the time s/he first arrives at the office. Picking up the equipment needed to do the day's activities is the first work activity of the day, and therefore the office is the first work site of the day.