Please read
JR pass exchange order is valid for 3 months from issue date.
The reason we ask you to put date(tentative plan) is to make sure you plan to activate it within 3 month or not.
You can start using your pass right away or you can also advise which day you want to start using your pass at the time of activation in JR exchange office.
NEWS 
Change of Business Hours for JAPAN RAIL PASS Exchange Office 【2021/04/09】
Most update infomation Please check here
New Business Hours as of April.01.2021
Information for foreign nationals visas 【2021/11/02】
Who are Non-Japanese passport holders, please check here before you travel to Japan.

Japan Covid-19 travel restrictions 
To find measure by the Government of Japan, please check here.