Medium term drift seems to be settling down a bit now. The mark and space on my signal is about 6Hz, so as can be seen from the 15min grab I took - compared to te datum line I inserted it looks as though it wanders +/- 2Hz over the time frame.

Carrying out a similar test against WWV frequency stanards  on assorted bands and against my 10MHz standard  shows a minimum  +/- 1Hz drift attributable to the RX itself so Im reasonably pleased with that.