How many hours can I work on Day 1 CPT - part-time or full-time?

It depends on the CPT authorization the school gives you: part-time CPT is 20 hours a week or less, full-time is more than 20, and the school's DSO decides which you get under its policy (some tie full-time CPT to your GPA). Full-time is common, but 12 months or more of full-time CPT at one degree level ends your OPT eligibility for that level. Tell me whether a future OPT matters to you and I'll factor it in.