Can you please wait for the invite?

I don't think it's unreasonable for people to start asking for details now: maybe your FMIL is booking a trip to her hair salon in the morning and needs to know the ceremony time, or booking transportation, etc. Guests would be looking to book hotels- maybe they are arranging check-in times around your ceremony time, etc.

If you already have the details on the website then I would politely remind them that they can find all the information there, but that not everything is set in stone yet... so they can check closer to the date for the final details.

I just told them in advance, it didn't bother me to do so. Our wedding website was ready basically a year out so sometimes I would send the link to people if they had questions too.

I have put everything on the website and keep telling everyone to refer to that, as it is easiest for me to update the info there than informing everyone individually. But she insists that I tell her in person as she believes that no one older than us will look at/have access to the website.

And there are things that have not be decided/booked/reserved yet, so I don't want to give out certain information that is not solidified, if there is a chance that it could change, because that might cause confusion.

YES. This. 100% this haha!

Yep, happened to us, but mostly with family! We ended up actually just sending invitations to our immediate families & bridal party super early (like 4 months before the wedding) because I knew they were all eager to make their plans and was sick of fielding all the questions

Yes, this happens to me all the time and were not even getting married until 2021. The only thing that gets on my nerves is when they were told possibilities (at the time nothing had been set in stone), they had a rude opinion about it.. so I stopped telling extended families details

I mean - it's your MIL. Why is it a big deal to just tell her? Or tell her it's not 100% but probably close to 2pm, or something like that. Lots of people don't use the websites.

Tell them to chill, these details are still up in the air, and it's on a need to know basis.