requirements for ALTP hours wise
(e) Experience— He shall produce evidence of having satisfactorily completed as
a Pilot of an aeroplane not less than one thousand five hundred hours of flight
time of which not less than one hundred fifty hours flight time shall be in the
preceding twelve months and his total flying experience shall include —
(i) not less than five hundred hours of flight time as Pilot-in-Command or
as Co-Pilot performing, under the supervision of a pilot who fulfills the
flying experience requirements of a check pilot, the duties and functions of
a pilot-in-command provided that at least two hundred hours out of these
shall be cross-country flight time, including not less than fifty hours of
flight time by night.
Note— Where an aeroplane is required to be operated with a co-pilot in
accordance with the provisions of the Flight Manual of the aeroplane, not
more than fifty percent of the co-pilot flight time shall be credited towards
the total flight time required for the issue of the licence, but not more than
fifty percent of the co-pilot flight time under supervision shall be credited
towards pilot-in-command flight experience required for issue of the
licence, and full credit for such flight time shall be given towards total
flight time required for issue of the licence.
(ii) not less than one thousand hours of total cross-country flight time;
(iii) not less than one hundred hours of flight time by night;
(iv) not less than one hundred hours of instrument time under actual or
simulated instrument conditions of which not less than fifty hours shall be
in actual flight;
(v) not less than[u] ten hours of flight time completed within a period of six
months immediately preceding the date of application for the licence.
So,you can see that it will be sometimnes before you are eligible for issue of a Licence.
But, you can always appear for the ALTP exams and complete them. Then later on when you got the hours , apply for the Licence.
Now, if you just passed the CPL first get an airline job or Instructor Job to get the hours. Corporate job may not give you that many hours within a reasonable short period comparatively
Once thats done, now start preparing on your own with the available books meanwhile getting used the actual airliner environment
Once you are experienced in the aviation environment for about 500 hours or so, I think that would be the right time to go join any of the reputed classes for ALTP , prepare and appear for the Exam.
Remember, once you are in an airline you will be utilised by them almost mercilessly since thats what they are paying you the big bucks for. So you got to find time for the classes.
Basically 500 hrs PIC is equal to 1000 hrs PIC under supervision of a checkpilot. Now thats going to take time. Now even if you do 70 hours a month, you might be flying with a check pilot for may be 25 hours a month conservatively.1000/25 means 40 months...almost 3plus years But actually it wont be that long since as you get more experience, your company itself will program you more and more witth the checkpilots for PIC hrs. So maybe at a guess it might be about 2.5 to 3 years by the time you become eligible.
If attending classes and doing your flightis inconvenient if you are not based at a place where you want to do your classes , you got to do more of self study and attend compressed courses with the reputed classes.