Plenty of people on here have given great suggestions. It's now up to you to decide whats the best for you to pull off. If the pot is too large to move twice a day then you def. need to build something around it to block light be it.. and tarp based, box based, or can based cover. I would come up with something that is a good size larger than the plant to allow for enough air during the dark cycle where there may possibly be little to no ventilation. It is not that important during the dark cycle to vent.. (I know some will argue this, but I have never vented my Dark Room tents during 12off and I get great yeilds from very healthy plants).
I would try to my hardest to keep it as close to 12/12 as possible. But pick a split that is 12 or more dark and stay on schedule from that point on... Also mimick what is going to best match natures actual 12/12 come end of summer/fall.
Pick up a farmers almanac (or just look it up online) to determine what sunrise and sunset wil be and plan your man made dark cycle around that.
This way when nature's 12/12 kicks in you can stop with the covering and uncovering and you plant is already on schedule....
In the future.. plan ahead. Dont start an outdoor grow in a region that is not warm enough for an 8 or more week flower time to complete unless you have the time and resources to run around covering and uncovering plants twice a day. If you are serious about growing look into an indoor setup where YOU play the role of mother nature.
Also from some of you previous questions..
It will not shcok your plant to go from extreme dark to extreme light. If it were thousand of indoor grows would be having issues.
What ever you do just stay consistent. Inconsistent environments do cause undue stress. such as constantly varying light levels and on/off times, eradic temps, large variations in pH etc etc,,,
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