Does the date for menstrual menses change, and how is the increase calculated?

If the bleeding lasts no less than (24) hours, but doesn’t exceed (15) days, and the purity interval between the two menses is no less than (15) days, then it is menstruation even if the date of menses changes, or its duration increases.

Generally speaking, I`m dutiful to my mother and opt for obeying her. However, she chose a certain girl to be my future wife, but I`m not pleased with her choice although that girl comes from a good family and enjoys good character. Should I obey my mother or choose another girl that lives up to my expectations?

Praise be to Allah the Lord of the Worlds.

One must obey their parents in whatever is in compliance with the teachings of Sharia and within one`s capacity. However, you aren`t to blame for not marrying that girl, but it is better that you tell your mother about that and it is preferable that you perform Istikharah prayer. And Allah The Almighty Knows Best.

Is a woman`s neck an Awrah (private part)?

All Perfect Praise is due to The Lord of The Worlds.

It is an Awrah, and it is forbidden for her to reveal it before non-Mahrams (Marriageable men). And Allah Knows Best.

Does the time of Fajr (dawn) prayer start after the first Athaan (call for prayer), or the second one?

All perfect praise be to Allah,The Lord of The Worlds                                                                                                                                                                    The time of Fajr prayer starts after the second Adhan. And Allah Knows Best.