Google OR-Tools: Driver breaks for hours of service regulations

Each driver (vehicle) needs a 30 min break after 8 hours on-duty. Referencing a previous issue, here is my code:

# Add breaks
node_visit_transit = {}
for n in range(routing.Size()):
    if n >= len(data['node_name']):
        node_visit_transit[n] = 0
    else:
        if n in data['pickups']:
            node_visit_transit[n] = int(data['load_time'][n])
        else:
            node_visit_transit[n] = int(data['unload_time'][n])

break_intervals = {}
for v in range(data['num_vehicles']):
    break_intervals[v] = [
        routing.solver().FixedDurationIntervalVar(
            MAX_TIME_BETWEEN_BREAKS, MAX_TIME_BETWEEN_BREAKS, BREAK_DURATION, False, 'Break for vehicle {}'.format(v))
        ]
    time_dimension.SetBreakIntervalsOfVehicle(
        break_intervals[v], v, node_visit_transit)

However, no solution is found when this snippet is added, whereas a solution existed previously. A few questions:

1. What is node_visit_transit used for? From the Github code it seems to account for some form of loading time (based on load demand), so I adapted it for load/unload time here.
2. Am I using FixedDurationIntervalVar correctly? I would like drivers to have a BREAK_DURATION break after they've been on duty for MAX_TIME_BETWEEN_BREAKS hours, regardless of start time. I'm concerned this is forcing them to take a break at the absolute time MAX_TIME_BETWEEN_BREAKS, i.e. if MAX_TIME_BETWEEN_BREAKS = 8 then they all take a break at 08:00.

It seems like someone has figured this out here, but there is no solution example.