According to XWB the pictures of MSN152 were taken on Aug 25th. In the same series of pictures you can see the City of Hamburg sailing off. She arrived yesterday in Saint Nazaire!
Indeed, the pictures show a MSN152 being sailed to Saint-Nazaire where the cockpit is to be mounted with the ForwadFuselage, hence we shouldn't see MSN152 before at least October...
MSN151 was spotted in the same state by mid-June, and still hasn't showed up in a convoy. I guess MSN151 also might not appear in a convoy before mid(or end?...)-September...
For reference usage, we've seen this before:
> MSN135, same part seen on November 13 in Saint-Nazaire and convoy started on January 28 > MSN141, same part seen on February 21 in Saint-Nazaire and convoy started on May 8 > MSN143, same part seen on April 2 in Saint-Nazaire and convoy started on June 19
That's around 10-11 weeks (~ 2.5 months) between arrival of the fuselage part and the start of the convoy.