Turn changes (also known as game ticks) are the basic unit of time in Nations. Important events happen during the turn change, ranging from production to deployment of units. There are many different intervals of the turn changes, the smallest lasting a measly 10 minutes with the largest turn changes last a whole hour (though day changes could also argued to be a turn).
All the Turn Changes (that I know of)
10 minute ticks
Every 10 minutes past the hour (GMT/UTC time) one 6th of your units military Upkeep is taken, and if healing is required, double of the hourly uptake is taken to heal 10%
Peacekeeping missions are sent at this time, and it doesn't matter if its send at 2:11 or 2:19, it would be sent at the same time, in this case 2:20, and the same can be said about the healing of units (As far as I can remember,) There are no other uses at this mark
Hour Game Changes
0 past the hour (GMT)
At the hour, every hour, your population upkeep will be used up, what consists of money (government if not Dictatorship, though money would be given then), power, and Consumer Goods.
At this stage, all things on your queue will go down an hour, and if less than hour, or complete, so it would be viable to build things at 7:59 am and 7:20 am (GMT/UTC), as they would be 'done' at the same time.
Another use of this ticks is for offers, all offers whether it be unit, officer, item shop or card pack shop, it would be timed against this, the time til the beginning, time remaining and ending of all sales will happen at this time too.
(Due to this many actions happening at this point, including all the 10 minute ticks, there may be a lag spike at this time)
(As far as I can remember,) no other uses of ticks at this time
30 Minutes past the hour
The only use of this tick is Foreign intelligence, where you loose your money at this time, and an hour 'passes'.
There is no tick for all factories, and all act independently, producing every half an hour exactly.
This is when all quests reset, you are allowed to Expand border again, events are generated (though will start the next time you log in), and Sales generate (there may be others). Due to so many things being updated at this point, there may be a delay at this point also
DM me on discord or say in the comments if there any others