If you make three times the national average gross salary: one month (fast-track: 15 days). If you make one and a half times the national average gross salary: two months (fast-track: one month).
A Blue Card may be issued to practitioners of the following professions on an expedited basis (30 days regular, 15 days fast-track), provided their labour contract is for at least one year and the salary is at least 1.5 times the national average.
*2019 Q4
If you are an EU citizen and are planning to stay for more than 3 months, you need to register to get an EU National Certificate from the Migration Center.