Earning your mechanic certificate takes 18 months if you want one rating (airframe, or powerplant), and 30 months if you want both ratings.
According to the FAA, your documented experience must be full time working on aircraft and performing the duties of mechanic:
§65.77 Experience requirements.
Each applicant for a mechanic certificate or rating must present either an appropriate graduation certificate or certificate of completion from a certificated aviation maintenance technician school or documentary evidence, satisfactory to the Administrator, of—
(a) At least 18 months of practical experience with the procedures, practices, materials, tools, machine tools, and equipment generally used in constructing, maintaining, or altering airframes, or powerplants appropriate to the rating sought; or
(b) At least 30 months of practical experience concurrently performing the duties appropriate to both the airframe and powerplant ratings.
The requirement for that experience to be equivalent to full time employment has been established by the FAA Chief Legal Counsel in letters of interpretation.
That's 18 months of experience for the airframe, or 18 months of experience for the powerplant, or 30 months of combined experience for both. Then the three maintenance knowledge exams (General, Airframe, Powerplant), and a practical test after obtaining your FAA authorizations to test.