No :) Megas can randomly hatch anytime, with an higher chance while
having a Mega Cuff activated (can be bought with Nuggets) and while
breeding Pokemon with good IVs. Shinies are hunted with the
Pokeradar, which can be used without Premium. You will need PD or
Electric Gems to activate the Pokeradar, and the charge will last
until you break the chain or hatch a shiny.
The advantage of having Premium is that the Pokeradar will keep
running if you hatch a Shiny, without having to start over.
In case of emergency Plushie