Sri Chandrasekhara Paramacharya of Kanchi Kamakoti Peetham said once that the proper time to do sandhyavandanam is hinted in the tamil saying " Kaanaamal konaamal kandu kodu". There is one important step in Sandhyavandhanam named Argya Pradhaanam (means giving Argyam to Sun God).
As per this Tamil saying this Argya Pradhaanam is to be given along with ...
Nothing happens after death to the atma which is merely a witness. It is the subtle body that is affected by death. Check Gita 2.17-2.22 for the answer to your question. For example, Gita 2.22 says,
'Just as a man gives up old garments and puts on new ones, so the
embodied self abandons decrepit bodies and assumes new ones.
What happens ...
No its not exactly in the mind but the Karmas are attached nonetheless to the Jiva till it attains liberation. So, its also not somewhere remote. (However, if you take into account Chitragupta keeping an account of our Karmas, then it's somewhere remote).
Devi Bhagavatam 7.30 says:
The Karma, auspicious and inauspicious, done in many previous lives