These qualities make a good journalist. There is no absolute answer to this question. The best time to apply for summer internships is probably late in November and December. By March, many positions are filled, but others do come up. There is no best time to apply for permanent employment.
Most openings occur when an employee takes another job.
In such cases, the editor is likely to need a replacement in two or three weeks. Perhaps, but he may not, or he may be more attentive to a letter from another applicant who wrote last week. On the other hand, those who do not write letters until they are ready to work often discover that most of the opening have been take. Coping with this dilemma requires foresight and effort. You should write prospective employers four or five months before you will be available.