How to handle date in js to work on iphones?

Question

JavaScript

It is necessary to calculate the difference in dates - "now" and timestamp from the database.
In fact, quite satisfied with the way

parseInt((new Date() - new Date(timestamp))/(60*60*1000))

But as always with the ill-fated iPhones, you need to invent something - for some reason you can’t set the date on them using new Date("2020-10-10 15:15:15"), it only works with a number in milliseconds. Is it possible to somehow convert the date to milliseconds without three-story splitting into parts and multiplying the components? Or maybe there is another option to pass the date to Date()?
Thanks in advance)