Hi,
Please check the following link for clear difference between all the AIPP streams and click on Read more.. to get the details about requirements for education and job requirements.
https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/atlantic-immigration-pilot/hire-immigrant/requirements.html
To get started, first of all your employer must be designated or willing to apply for designation under AIPP. Secondly, the employer should submit your endorsement application for which you will require IELTS General scores. Processing times may vary from 3 to 16 weeks.
For AIGP, You are eligible if the standard completion time of you degree is 2 years (and you university can give you a degree completion letter stating this) and you have completed it within 24 months from the day you apply for PR (excluding the endorsement process) but you will require a job that will last for at least 1 year from the date you PR application was submitted.
For AHSP, You will require 1560 hours of work experience within last 3 years. For job offer - "The employer is offering you a job that will last for at least 1 year (one year from the time you become a permanent resident). "
For AISP, You will require 1560 hours of work experience within last 3 years. For job offer - "Your employment is permanent, that is, there is no set end date."
You can start the process with IELTS because its valid for 2 years. I would say first wait to see for how long your PGWP is approved for because the process has changed since Feb 2019 and at the same time look for a job with at least 2-3 years time committment or a permanent job(some employers may offer a permanent job) with a designated employer before you start any process. Your job offer duration may also depend on the duration of your work permit (depends on the employer).
Each step beginning endorsement to PR application will take time. At the moment the response to applications in general are delayed. The other route could be wait for 1 year to gain Canadian experience and apply under Express Entry - Canadian Experience Class. You can also contact your provincial immigration office for more details.
For further questions, you can post your queries on the following thread:
https://www.canadavisa.com/canada-immigration-discussion-board/threads/atlantic-international-graduate-program-aigp-timelines-and-queries.673153/
P.S.: I am not an expert