About making reservations

Hi there

I'm heading over to Japan the third time in may 2018, but the first time with my girlfriend.
That's why we would like to eat in some regular (or you could say a bit more expensive) restaurants.

I already did researching and know which ones we would like to visit

Tokyo:
Umegaoka Sushi No Midori Sohonten Shibuya

Kyoto:
Tempura Endo Yasaka Honten
Premium Pound Sanjo Kiyamachi

Osaka:
Kani Douraku, Dotomori Honten


So my question is:
How long in advance do you have to make reservations?
(It's still 3 months before we even go...

Can I just ask them by mail?

well generally one week before is enough, but you might call them even right now and ask if they can reserve those slot for you...