How time intensive or how long can an ISR be?
How long can an interrupt be?


If you don't want anything else to happen, then as long as the time between successive interrupts.


  would it stop reading the sensor when the code is interrupted and for how long.


While the interrupt is running nothing else can happen in software. Absolutely nothing. Only one thing ever happens at once - either your main loop or the interrupt. For the entire duration of your interrupt everything else is put on hold.

That includes things that rely on other interrupts to function, such as serial communications, millis() and delay(), etc. That means using such functions from within your interrupt handler is a big no-go.

It is generally very very bad practice to have an interrupt blocking for more time than absolutely necessary (a few milliseconds or even less). If you need to have things taking a long time then you should consider breaking them down into smaller operations and doing different sections at different times through different means.