WoWs premium time is coming on Patch 7.12!
As of 0846EST there still is no message on the main WoWs page, so patch 7.12 is looking to drop Dec 19th. You have a week to suss out which way you want to go with premium time.
So this means that you will have two set of premium time. WG premium time and WoWs premium time equal to the amount of premium time you have at the time. In my case, today I have 218 days of premium time, so on Wed, Dec 19th after patch 7.12 drops, I will have 210 days WG premium time and 210 days WoWs premium time that will overlap. NOTE: doubloon bonus is not active for this free WoWs premium time overlap, only for new WoWs premium time overlaps. See more below.
So being able to have 3 Campaign tasks instead of two, will be the same in either premium time. Same with the premium port being selectable in both premium times. (Note: Premium port is just a pretty and provides no extra benefits. Hawai'i used to the be the premium port)
In the examples above, only first win, flags, camo and the premium time bonues were counted. You will get clan, combat missions and other bonuses like normal, but these examples were kept simple.
While it doesn't look like much for one battle, every battle you play with a WoWs premium account will have that extra bit of XP and it will add up over time.
This is important. Premium time that you have that has WoWs premium time added on patch 7.12, will NOT do the doubloon compensation overlap for that dual premium time. Any new premium time that overlaps will get the doubloon bonus as seen below.
The compensation in doubloons is only for WoWs premium time that overlaps with existing WG premium time.
For example, I will have 210 days premium time when patch 7.12 drops. So after 7.12 drops, I will have 210 days WG premium time and 210 days of WoWs premium time and that WoWs premium time will not get doubloon compensation as it was free. So say I buy 180 days of WG premium time. I will now have 390 days of WG premium time for all three games and 210 days WoWs premium time. If I buy more WoWs premium time the next day, say 90 days WoWs premium time, then I would have 389 days of WG premium time and 299 days of WoWs premium time and I would get 2,250 doubloons for the WoWs overlap with WG premium time.
But lets say I buy them in reverse. I will have 210 days premium time when patch 7.12 drops. So after 7.12 drops, I will have 210 days WG premium time and 210 days of WoWs premium time and that WoWs premium time will not get doubloon compensation as it was free. So say I buy 180 days of WOWs premium time. I will now have 210 days of WG premium time for all three games and 390 days WoWs premium time. If I buy more WG premium time the next day, say 90 days WoT premium time, then I would have 299 days of WG premium time and 389 days of WoWs premium time and I would NOT, REPEAT NOT, get 2,250 doubloons for the WG overlap with WoWs premium time.
Let's look at some more examples.
Say I have no premium time. After patch 7.12 drops I buy 360 days of WG premium time. Then 10 days later, I buy 360 days of WoWs premium time. So I would have 350 days WG premium time for all three games and 360 days of WoWs premium time with the +15% bonus. During that time 350 days of WoWs premium time would be overlapping with the existing WG premium time, so I would get 8,750 doubloons when I bought the WoWs premium time as compensation. Not a great way to farm doubloons, but if you have to have that extra +15% WoWs XP AND WOT & WoWP premium time at the same time, you get some compensation.
But if you buy them in reverse, you do not get the doubloon compensation as the WoWs premium time was bought before the WOT premium time.
So if you are going to buy both premium times, ALWAYS buy the WG premium time first.
So for that 5 star operation that gives out a day of premium time. Or the Science of Victory campaign that gives out 7 days premium time. Or that super container that gives you 14 days premium time. They will all be WoWs premium time. So if you have WG premium time, then the reward premium time will overlap. It will NOT extend WG premium time. It will extend WoWs premium time.
If you only ever want to play WoWs, then get WoWs premium time.
If you want to play WoT/WoWP as well with premium time, then get WG premium time. Just note that any premium time you get in WoWs will be WoWs premium time and will overlap with any existing WG premium time.
Dec 20th, 2018 Edit: @Radar_X has said that Warships premium time in the shop has been delayed and will be out later this week. Warship premium time for doubloons in-game is working.