Entry clearance vignettes allow holders of UK residence visas to enter the country and collect their biometric residence permit. They are issued for a period of 90 days, during the pandemic, this period was extended from 30 days.
If you are unable to enter the UK before your vignette expires, you can apply for a replacement without having to submit a new visa application, provided that your leave to enter has not expired. The replacement application costs £154 and requires attending a biometric appointment. A decision on your application should be made within three weeks.