Deadline to pick up Czech Employee Card?

I just got my employee card approved (after 175 days), so I'll have to pick it up in Prague at the Immigration Office.

Question: Does anyone know if there is a deadline for picking up the employee card? I would like to fly to Prague in mid-February (so almost 4 months from now), but will come sooner if there's a chance the employee card will expire. I called the immigration office but couldn't get a satisfactory answer, just a worrying non-commitment like "oh probably, call when you're in Prague".  I would like to hear someone's experience, otherwise the "oh probably" is going to keep me awake at night for the next four months!

BTW my employers are flexible as to my start-date, so no worries there. Thanks for any information!