I did this in May and yes it was qute a balance between daylight hours and tide which will give you the much needed boost. If you have a decent
engine it should not be a problem but certainly 11 or 12 hours as it took me in my
small boat. I stayed in Hornfluer and came out early with the high tide.
I read there is a place but not advised as mainly for
commercial vessels.
I would also contact Rouen marina as its not so large and may be busy. I stayed there for three nights and they were very helpful.
Ensure you have the VNF vignette prior to entering the Siene. Safe sailing