I haven't found any clear information on this topic when I applied for such e-visa, and now I'm paying the price for a mistake I made. The e-visa for Saint Petersburg and Leningrad Oblast is still experimental, so there isn't lot of information available to it. So I hope this will help future travellers.
So, what do I have to take care of or watch out for when applying for the new e-visa for Leningrad Oblast?
First of all, I recommend: apply for a normal visa if you're not sure what you're doing.
Basically, this e-visa is very comfortable to apply for and a really nice option if you're planning to stay only for a few days. So, what can be the problems with this visa?
You are only allowed to enter and leave at certain points, which are listed at the official website. This also means that you're not allowed to use a flight that has a stop anywhere in the Russian Federation (e.g. Moscow).
You are only allowed to stay a maximum of 192 hours, beginning at 0:00 AM the day you're arriving. Not from the moment you enter the Russian Federation.
It is not possible to extend an e-visa.
You can't leave and reenter the country with an e-visa. Once you leave, the validity of the visa ends.
This means that you absolutly have to exit before 23:59 seven days after your arrival. If you reach the border checkpoint only seconds after midnight, you won't be allowed to leave.
If you can't leave Leningrad Oblast on these terms, no matter the reason (delay at the border, cancelled flight, illness, delay of the flight/bus/etc..., personal miscalculation, etc...), you will not be allowed to leave the country on your own terms.
If you fail to leave on time, a five year ban from entering the Russian Federation is very likely.
I will answer how to deal with this situation in a separate question. Please add if I forgot to mention anything.
It does not work when entering by rail (Jan 2020). Thus, make sure you are not planning to enter or exit by rail.
Make extra sure that the exact Latin name spelling in your visa applications matches the spelling in the machine readable section of your passport. Especially if you have any diacritics in your name. They will absolutely refuse your entry over a single incorrect glyph - a lot of complaints about that.
When in any doubt, make sure it matches the Latin spelling in the white bottom block with a lot of <'s.