No penalty. You get rewarded for your accepted share over the last n shares when the block is found.
Yours shares on the weekend will be counted if a block is found while you are not mining on Monday.
You not mining all daytime Friday will reflect if a block is found on the weekend with its 5n look back (currently ~4days 9hrs.).
It averages itself out to an effective hashrate "Your N Avg" for mining.
I am not yet entirely convinced that it averages itself out and am working on a calculation. I believe that there is a disadvantage for sporadic miners and newbies, anyone who has not filled the 5Nd window with a flatline hashrate. Once I have my results I will publish here.
There isn't.
The way to see that is by looking at shares, which is how the pool works.
It is basically understanding PPLNS which is fixed on "N" shares.
When you submit a share, it is paid the same way no matter how much hash rate you have and no matter how many other shares you submit.
Again, as it says on the web site:
The 5Nd means the pool rewards 5 times the expected number of shares, each time a block is found.
So each share will be paid approximately 1/5 of it's expected value, in each block it gets a reward,
but each share is also expected, on average, to be rewarded 5 times in blocks found after the share is submitted to the pool.
The last line is the clincher.
Also, the reward is based on the pool finding 5Nd shares.
The higher the total hash rate, the more blocks are expected to be found.
But that 5Nd decides who gets rewarded, not any share to share effect.
If you submitted 1,000,000Diff shares in the 5Nd, you'd get X reward.
If tou submitted 2,000,000Diff shares in the 5Nd, you'd get 2X reward.
The number of times any share is rewarded is dependent upon when that single share was submitted, not based on any other shares.
Lastly, there's the "N side effect" reward result that seems to help people understand the above details.
When you stop mining, you keep getting new (diminishing) rewards for all blocks found in the 5Nd after you stop mining, while each share you already submitted is still inside the 5Nd range of any future blocks found.
The bottom line is, if you look at how a single share is rewarded, it clearly explains that hopping and on/off mining has no expected effect to disadvantage it.