How long does it take to update the domain name servers?
 

I have switched to another hosting company and now I have 4 name servers in my domain accoun (2 from the old hosting and 2 from the new). I would like to know when can I remove the old name servers?

2days

The changes should be extensively propagated within 24-hours,
but this can vary. 3-days should be safe.

If you're switching domain name servers along with your site move then you don't want the old ones linked to your domain at all. If you have two sets of name servers returning different results for the same query then you're going to get some pretty strange things happening.

24-48 hours although our last site was all hooked up in about 13 ours flat :)