22.9: Competitors who are late for their start time shall be permitted to start. Their new start time must be recorded.
• In a mass or chasing start, the competitor shall be started as soon as possible.
• In an interval start, if the competitor is at the start line less than half the start interval after their start time they shall start immediately.
• If the competitor is at the start line more than half the start interval after their start time they shall start at the next available half start interval.
The above is taken from IOF Rules so, had the race been a WRE, it is clear that the 2nd and 3rd bullet points would have applied and the runner would have been set off on the soonest half minute (or immediately if the start time had been missed by less than 30s).
BOF Rules have not yet caught up with IOF ones ...