Quite possibly.
Generally air can have properties of instability. With the right ingredients, warm sun and chuck in some moisture, mountains helping this warm/moist air rise and you can get large unstable clouds and sometimes thunderstorms.
The air around these storms and in the area around this cloud can/could be turbulent.
There is no hard and fast rule. it can all be dependent on so many variables. such as temperature, wind strength and direction, level of instability.
But if there were storms in the area a short time ago it is possible that the air may still be turbulent long after the storms have cleared.
Although this may not be the reason for the turbulence what so ever! It could be a number of things after 6hrs...A few example are-
Strong Jet stream
Steep temperature gradient over a short distance
mountain waves
flying across a cold front
so it could be coincidental that there were thunderstorms in that area 6hrs before hand or it could be connected.
hope this is not too confusing and helps you understand a bit about the weather.
Don't ever feel threatened about the safety of the aircraft in turbulent skies. it may feel uncomfortable but aircraft are built to withstand unbelievably strong forces.
