As already mentioned:
@Tyler_Kaye, also confirms it is better to store timestamp in the native format and to apply the business use-case formatting at the presentation layer in your other thread Timestamp in require format - #4 by Tyler_Kaye
As he wrote:
just store the field as a Date which is supported in MongoDB and is most often the better thing to do when storing a date in the database. Your client-side application can be in charge of how it wants to convert a date into a string