Overstayers must adhere to strict time constraints when applying for ILR. They have only 14 days from the expiry of their previous leave to submit a new application, and this period is non-negotiable. If an application is refused, there is a 14-day window to apply again, but this must be done within 28 days of the refusal. Missing these deadlines can lead to being considered an overstayer, with all the associated consequences.