Shabbat question

Hi, I have a quick question for the community and hope you can help?

I’m of non-jewish decent/beliefs and I have a friend I am close with who is Jewish. We live in 2 separate time zones around the world and I was asked not to msg them during their Shabbat period which I want to respect.

Can someone explain if this counts as the Shabbat in just their time zone or is it in my time zone or is it both?

I care very much about this friend but the way our time zones are spaced out this means not being able to msg each other for so long if it’s both. :0(

Could someone please answer this and explain how this works?

Thank you.