There are twelve months to commence proceedings for summary only offences in Scotland currently, temporarily extended from six months as part of Coronavirus measures.

That doesn't mean that you must hear back within 12 months, just that the relevant administrative steps have been taken in the background. It could be longer than that before you actually receive anything.

There is a significant backlog of samples awaiting analysis by labs at the moment (discussed here) so I would expect the sample to be analysed much closer to the end of that time period than the start.