refactor: modify date, startTime and endTime format

[adarshaacharya]

for now date, startTime and endTime are stored as string, which i believe isn't good for long term, and validation pipeline is also setup on backend as string. I want to refactor such that it will be stored in the normal form and while retrieving on client side only moment will format it. It will help to customize the date/time format on future if needed. Thank you.