my CKC spaniel first came to season at 10 months and can be anything between 6-9 months between each cycle. my shih tzu first came at 5 months and is roughly every 5-6 months. But, strangely her summer season came early last year (whilst we were on holiday!) and this year it came again exactly a year to the day! How weird!?!
And they sometimes sync in with each other, either coming on one after the other or a week into one, the other will start but the CKC syncs in with my shih tzu not other way round