how often does namecheap update NS
 

changed my ns before with them and it was almost immediate. today the must be on vacation?

Remember, however fast they do it, other DNS servers only update every few days, so it will take that long for the entire Internet to "know" about the change.

namecheap is an enom reseller which pushes root server updates every half hour. However, you still have propogation and caching delays due to the configuration of the prior dns and servers that may cache beyond the prior dns's settings.

Generally speaking, 24 hours sees about 70%, 48 hours sees about 90% moved and up to 7 days for 100% propogation is the rule of thumb that I use.