I wrote to 6 professors whose research aligns with my interests (all in Europe) on December 21 for disussing PhD opportunities and attached my CV along with the mail. One of the professors replied after 3 hours that he doesn't have an opening. The rest have yet to reply. I came to know that it is also holiday season in Europe. I am from Asia.
How long should I wait before sending a reminder E-mail given that it is holidays there?
In general, how much time it takes a professor to reply to an e-mail of a potential PhD candidate?