Baptism in Advent

Yes, baptism can take place during Advent. There is no Church rule that forbids it. In fact, canon 856 explicitly states that baptism can take place on any day, though it recommends Sundays.

The only days where we find a rule forbidding sacraments are Good Friday and Holy Saturday until the Vigil (Paschalis Solemnitatis 61 & 75).  And even then, the baptism of someone in danger of death is permitted.