Non-EU students face a weekly hour cap that cannot be averaged out across quiet and busy weeks, plus a work permit the employer, not the student, has to arrange. Employers unfamiliar with that process often decline rather than deal with it, which students tend to read as a rejection of them personally.
Sixteen hours a week during term time, full stop — not an average, not bankable, so 30 hours one week and nothing the next isn't allowed, and hours across multiple part-time jobs get added together against that same cap. The exception is summer: June, July and August you can work full-time. Either way, the hour limit isn't really yours to manage — your employer has to hold a TWV (tewerkstellingsvergunning, work permit) for you before you start, applied for through UWV, and it's tied to that specific employer and role. There's no fee and no labour-market test for hiring a registered student, but plenty of employers still don't know the process and will hesitate or decline rather than deal with it, which is worth knowing before you take a rejection personally. One real exception: an unpaid internship that's a mandatory part of your curriculum doesn't need a TWV at all, since it isn't employment in the legal sense — a paid one does. Fines for employers who skip the permit are steep, which is exactly why some genuinely can't take you on informally. If you're unsure whether an offer counts as term-time or summer-rate hours, or whether an internship is paid or unpaid, your university's international office can confirm before you sign anything.