Conditions for the validity of Salaah

Q: My mom said that we should not pray fajar prayer right after adhaan and we should wait for 15 minutes. Is it true and if it then what's the reason behind this?

Q: “Quarter of the head is approximately the amount of the palm with the fingers.” So to estimate this, do I place my hand vertically on my head or horizontally?

What if some of my hair is showing and some of my awrah from my arm is showing? Do I need to add them up together? 

Q: I’ve noticed that in fard wudu, only a quarter of your head needs to me washed. And when awrah is shown during salah, then only if it is under a quarter, the salah is deemed valid.

Today a little strand of my hair was showing during salah. I’d like to know how to measure a quarter of my head.

Q: A few men performing jamaat salaah in the masjid or individual salaah at home where there's small lizard's faeces scattered around. It got smeared on their palms, knees, etc. with or without their knowledge. Will their salaah be valid? Is the faeces of small lizard's clean or unclean?

Q: I performed the 1st rakaat of a salaah individually with an unclean (impure) trouser but I realized this during the 2nd rakaat. What do I have to do to correct the salaah ?

Q: Is the namaaz accepted if one is using perfume, using perfume for namaz is permissible?

Q: If a woman performs salah with 3/4 length trousers and then tights under them, wherein no part of her leg is visible, is her salah valid?

Q: If Fajr time expires at 7:08am and I finished my salah at 7:08 am, is my salah valid or I have to offer qadha for it?

Q: I want to know that what should be the correct timing to pray ishraq prayer? How much time after fajar aazan can we perform it?

Q: In Ssaudi the Adhaan is given at the very moment the salah time enters. In India, except for maghrib, there is a delay in the Adhaan being given for all the other 4 salah. The delay varies from places. Suppose Bangalore Asr time sets in at 4.04 pm but Adhaan is called at 4.30 and jamaat starts at 4.45 pm.

My question is, should the sunnah be offered after Adhaan or can one offer the sunnah once the time of the salah enters even before the Adhaan is called out?