How much does it take for a prayer bump to appear? Would I have one if I have a lengthy (about half an hour) sajdah every day? How can it be erased?
All perfect praise be to Allah
First of all, i should tell at first look i didn't like your question, but than i thaught i think it is good if someone has desire to have one because quran says:
محمد رسول الله والذين معه اشداء على الكفار رحماء بينهم تراهم ركعا سجدا يبتغون فضلا من الله ورضوانا سيماهم في وجوههم من اثر السجود ذلك مثلهم في التوراة ومثلهم في الانجيل كزرع اخرج شطاه فازره فاستغلظ فاستوى على سوقه يعجب الزراع ليغيظ بهم الكفار وعد الله الذين امنوا وعملوا الصالحات منهم مغفرة واجرا عظيما
Muhammad is the Messenger of Allah ; and those with him are forceful against the disbelievers, merciful among themselves. You see them bowing and prostrating [in prayer], seeking bounty from Allah and [His] pleasure. Their mark is on their faces from the trace of prostration. That is their description in the Torah. And their description in the Gospel is as a plant which produces its offshoots and strengthens them so they grow firm and stand upon their stalks, delighting the sowers - so that Allah may enrage by them the disbelievers. Allah has promised those who believe and do righteous deeds among them forgiveness and a great reward. Quran 48/29
So, answering your questions one by one.
1- No i don't yet have one.
2- HOW are in many ways, it depends on the material/surface where you do sujood, and how often you pray and how much you pray(i mean nawafil etc).
3- It still depends(sometimes also on person, some people don't get it in all their life. And don't confuse it from the verse above that if somone does not get it than he is not one of them, verse is general, and in that times, their were no soft carpets etc in masajid, so usually people who prayed five times a day would had them easily.)
4- This can only be answered by skin doctors.