Perhaps you should ask your colleagues. I don't think any of us would know what they have done!
You have already heard what other forum members have said, but lets put some numbers around this. On 1 Oct, sunset at Roncesvalles will be about 1947, and civil twilight will end about 30 minutes later at 2018. Barring weather effects, if you leave SJPP around 1430, you will have a bit over five hours of daylight, and not quite six hours where you might be able to walk without artificial lighting. But you will also be walking through wooded areas that will be darker earlier.
Based on a gpx track from the Spanish mapping agency, I estimate the flat equivalent distance for Route Napoleon to be about 39 km. At 6 km/hr, that would be the equivalent of 6.5 hours walking. If you take even as short a break as 30 min, you will need 7.0 hours, and this will mean arriving well after the end of civil twilight.
By mid-Oct, sunset and the end of civil twilight will be about 30 minutes earlier.
note:
Brierley suggests the flat equivalent for someone walking at 3 km/hr is 31 km based on an extra 10 min for every 100m of climb. Adjusting his calculations for your faster pace results in a flat equivalent of 39.33 km. I come at this a slightly simpler way, but with a very similar result, 38.72 km.
It seems that your own duration estimate is 4.5 hours. That would equate to a flat terrain speed of about 8.7 km/hr. I don't think that is very realistic as a planning speed.