When it's NTLM, extremely easy. I know NTLMv1 cracks at around 25 billion attempts per second on a high-end GPU, which is MD4 based. NTMLv2 is MD5 based with a longer key, so it's slower, I'm not sure how much slower, but I'll guess 1 order of magnitude. Still, far too fast for a password hash.
Given that far too many passwords can be found with a dictionary attack, it probably only takes seconds for an attacker with "several modern video cards"[1] of hashing power.
If your password is common (see something like https://github.com/danielmiessler/SecLists/tree/master/Passw...) or <10 ASCII characters, it shouldn't take too long.