How long dependents have to stay on first entry in UK

[ukncl]

Hello,

I would be getting General Tier 2 UK VISA by mid if Nov-2013. The VISA is being processed for my dependents as well with a start date of Jan-2014.
I would be travelling first week of Dec-2013 and my dependents will join sometime end of January 2014.
My question is how long they have to stay in UK before moving out for few months ? Is there any restriction.

I was told that the dependents had to travel within 3 months of getting the work permit and hence planning to have them travel earlier in Jan. My intention was to have them by end of Jun 2014 only after school closing here in India but given all these restrictions can some one please tell me how long the dependents have to stay in UK before leaving for few months for a vacation ? (between Mar to Jun)

Thanks,
Seenu