It depends on the company. Topps automatically puts a date six months in advance whether they have the redemption ready or if they haven't even made the card yet. A lot of their cards need a signature from the player which they haven't received back yet. What company is your redemption from?
I had 2 from Upper Deck. Redeemed them last year (October). They told me 8-12 weeks initially. That came and went. They told me they were backed up and to wait another 8 weeks. I waited and still nothing. I requested a replacement and they sent the first one right at 12 weeks upon my request. Still waiting on the 2nd replacement.
This whole process has kinda turned me away from redemptions now, especially the way Upper Deck has handled it.
Over the past 7 years I have waited anywhere between 6 weeks to over a year. I have redeemed cards from Topps, UD, and Donruss/Panini and surprisingly, UD has the best track record by far (both of the others never ended up getting the stuff signed and sent JUNK replacements.