- How much longer could it take to get our green cards? Some of us have to move back to Pakistan in about 30 days due to some personal
It's hard to say, but how long it takes for you to get the card should not have any effect on any of your plans. You already became a permanent resident the moment you entered the US with your immigrant visa. The immigrant visa, upon being stamped on entry, is no longer a visa (immigrant visas are single use anyway), but rather turned into a temporary green card (I-551) valid for one year from the date of entry. This is equivalent to the plastic card (which is also an I-551) in every way, for all purposes, including working and traveling.
And even if you don't have the plastic card beyond a year (it shouldn't take that long, but it's possible for it to get lost, etc.), as a permanent resident you can always go into a USCIS office and get an I-551 stamp which again will be valid for one year and you can use it for all purposes.
Make sure to never describe your immigrant visa as a "visa" anymore because that will confuse people who will look at its expiration date. (The visa is invalid anyway.) Rather, always describe it as proof of permanent residence.
- I know a green card expires in 6 months if you stay outside the U.S. How many days would it take if we apply for extensions of our
green cards after we receive them?
There is no such thing. The card expires in 10 years, and can be renewed when it's about to expire. Your permanent resident status never expires, even if the card is expired. Your permanent resident status can however be lost if you fail to maintain residence in the US (regardless of whether you have a valid card or not). There is no set amount of time outside the US that determines failure to maintain residence. It is determined by the totality of the circumstances and your intentions.
Separately, an I-551 (whether the plastic card, stamp, or endorsed immigrant visa) by itself, without anything else, is valid for re-entry after an absence of at most 1 year. If you get a Re-entry Permit, it is valid for re-entry for the duration of validity of the Re-entry Permit (a Re-entry Permit has a validity of at most 2 years). CBP may, however, admit you at their discretion even if you don't meet the above requirements.
Note that the above documents are valid for re-entry given that you haven't abandoned permanent residency by failing to maintain residence. If CBP determines that you have abandoned permanent residency, then they can put you into removal proceedings no matter how short your absence was.
- How many times can we get extensions of the green cards? 2 years? or more?
It can be renewed infinite times. Each time the card will be valid for 10 years.