Any twinkling of the stars or planets is an indication that the light travelling from these objects through the atmosphere is being refracted in different angles as it hits different layers both cold and warm air. The more turbulence in the atmosphere the more twinkling.
I would expect the planets to be more stable because they are not pinpoints of light, but actual reflected discs. So in answer to your question, from this backyard hack, if the planets are furiously twinkling, yes it probably bad seeing.
I am sure there are more expert members here who will confirm or deny.
Yes, I would have to say the same. The planet generally don't twinkle unless they are right down low on the horizon, where everything twinkles, so if they're twinkling overhead its rotten seeing!
If the Planet is twinkling and it's not close to the horizon where it's passing through a greater depth of disturbed air then Yes the seeing is very poor.
Some things you might want to check though
From your observing position ,looking visually at the planet, what is on the ground in that direction?
Are you looking over your house roof or one of the neighbours? The amount of heat escaping through the roof and the effect on the air (and thus the seeing) is remarkable!
Do you have substantial amounts of Concrete or Water (or even a main road - a problem I had in Terrigal) on the ground in the line of sight?
I just stood on our back deck having a cig (in Wamberal) looking out towards Terrigal (apologies to our non Central Coast members) and the lights in Terrigal are dancing. I'd put this down to looking over the roofs of a number of houses and the heat rising from Terrigal Lagoon - which is in my line of sight - so you need to be aware of heat sources on the ground between you and the object of interest.
Can you take a stroll close by where you have a lot of grass/no houses/no water/no concrete etc in your line of site - does the planet still twinkle? That should let you know if you have an issue with heat sources from your observing spot up to the ecliptic or whether you just have generally bad poor seeing on the night involved.
