Is it permissible for those coming for Hajj or Umrah to stay in Jeddah for three days and then enter into a state of Ihram from there?

This action is incorrect. It is obligatory to enter into a state of ihram from the miqat. So, whoever passes it without ihram must return to it. Otherwise, he must sacrifice a sheep to be distributed among the poor of Mecca. Sheikh Ibn Baz stated that it is obligatory for those coming for Hajj or Umrah to return to the miqat. Whoever passes the miqat without ihram is liable for a sacrifice (dam) that is sufficient for an Eid sacrifice, to be slaughtered and distributed among the poor of Mecca.