ANSWER:

No, you cannot pray any voluntary salah after Asr until the sun sets and not after Fajr until the sun rises. 

https://islamqa.info/en/109254

 

Can you do 2 nafal or more than that at any time of the day and there are no restrictions like for eg… After Asr there is no prayer until maghrib so can you pray nafal then or not????

Prayer | June 30, 2018 5:10 am
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Sheikh, i know about the 17 fard rakahs and 12 highly recommended sunnah units. Here in Pakistan for e.g we offer 17 rakahs for isha salah alone. We offer 4 units sunnah before 4 fard of esha and after 2 recommended units of esha we offer 2 nawafil as part of isha prayer. And after offering 3 witr we again offer 2 nafl as part of isha prayer! where is it mentioned to offer these
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I have realized that some people in my area recite a certain dua loudlyanytime the imam recites Surat Al tin in prayers. pls is that acceptable?