Is bio-metric got to be done in 15 days

hi every 1
just wanted to ask one question, hope to get the answer,
i wanted to know when some one receive bio-metric invitation letter , on letter its sy to contact for appointment within 15 days,
is that mean
1)u have to call for appointment within 15 working day ...appointmnet could be for whenever, or
you have to have bio-metric taken between 15 working days after the date on the letter????
thanks

you need to schedule it within 15 days.Thats al. If nothing is available, u choose the next soonest option.

its not your fault if everything is booked and UKBA recognise that

You have