Depending on how much crypto specialties you would want to cover, I'd say 2-5 years.
 First, you need to get the general concept of blockchain technology. edx has a wonderful short-course on this. that course is free to take and would enlighten you on how blockchain works. trust me, you would want to truly understand this if you want to be a crypto consultant, regardless of which specialty you choose. this should take roughly two months

Some specialties you might decide to look into include

crypto marketing: to become a crypto marketer, you need to be a good copywriter. I'd recommend makepeace course on copywriting. then you need to learn about facebook ads, seo, bicointalk advertising, and email marketing udacity course or HubSpot free courses are a great start.

Crypto-economist: the success of any cryptoproject depends on their crypto-economics. deciding to become a crypto economist keeps on on the verge of being a hot cake. to become a crypto-economist, you can start by taking general economics classes for free online.