Are fasts broken if you don't follow imsak timing?

Question

I just found out that my previous fasts might not be valid but please help me confirm if it's true or not.

Whenever I want to fast, I have suhoor until fajr time. My friend tells me that's wrong and my fast is broken because I didn't follow the imsak time which is approximately 10 minutes because fajr time.

For example: If fajr time is 6:10, then imsak time is 6:00. So I should stop eating and drinking at imsak time.

Is this true? If it is true and I didn't know about it, are my previous fasts valid?

Answer 1

You can eat up to the time for true dawn. This is the same as the starting time of fajr as you might find in a correct calendar or app.

وكلوا واشربوا حتى يتبين لكم الخيط الأبيض من الخيط الأسود من الفجر

And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night].

^{— Quran 2:187}

كلوا واشربوا حتى يؤذن ابن أم مكتوم، فإنه لا يؤذن حتى يطلع الفجر

Carry on taking your meals (eat and drink) till Ibn Um Maktum pronounces the Adhan, for he does not pronounce it till it is dawn.

^{— Bukhari}

Stopping earlier might be suggested by some for safety - i.e. to make sure you are not unknowingly eating when the time is over. However this is not required and your fast is valid.