File ASAP. You need to file so he can qualify for Medicare(takes 2 yrs after declared SSDI disabled).
The LTD carrier benefits if your husband wins SSDI because they would get their money back(except for probably 100 dollars a month-check your policy).
My LTD pays till I'm 65. I get reviewed once a year.
If your husband has a standing job and can't stand for 6 out of 8 hrs,that's usually a slam dunk for SSDI.Plus since he's in his 50's-it's much easier to win SSDI.