I don't see why you would need multiple tabs for timing... I've done ops before where I've had several cities within seconds of each other's time (I tend to clump cities) and have done just fine with only one tab.
I don't mind giving away my technique either (not like I haven't taught enough players how to do this). Doesn't use any premium, so there should be no issues there (given, though, I personally sometimes use the attack planner just for myself, to get a starting time without having to think too hard).
1) I pick a target
2) I figure out what cities I will be sending from/what I am sending from each.
3) I open notepad on my computer and put it in a list like this (Xs, of course, filled in with the actual numbers):
~~City 1: LU ATTACK X LU X LS
~~City 2: LS ATTACK X LS
~~City 3: BR SUPPORT X BR
~~City 4: LU SUPPORT X LU
~~City 5: CS ATTACK X ESCORT
with, of course, however many cities I'm using.
4) I open the attack window and find out the timing for each wave, notating it in the notepad next to each.
5) I rearrange the cities so they are in order, from longest time to shortest time away from the target.
6) I launch the first attack at whatever time I decide to do this. I open the command overview with admin (though I have done this just opening the attack itself, without premium), and the attack window in the next timed city on the notepad, and wait until they match. Then send. Repeat until everything is sent.
It's a little more time intensive, sure, but works just fine for me.
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Also to address something someone was saying earlier, about too many windows being opened and it closing all of them: This used to annoy me greatly (as I enjoy collecting statistics) until I went spelunking in the settings and found that you can set it so you can open up to 10 windows at a time (rather than the 5 that is default). So far I have never gone that high
Toria