Considering that India and Pakistan went to war right after independence, I can’t really see how this played out – especially since no peace treaty has been signed and India and Pakistan had no official relationship with each other until 2003.
One way to settle it is to look at what time India used pre-1948. From the timezone file:
India
Zone NAME GMTOFF RULES FORMAT [UNTIL]
Zone Asia/Kolkata 5:53:28 - LMT 1880 # Kolkata
5:53:20 - HMT 1941 Oct # Howrah Time?
6:30 - BURT 1942 May 15 # Burma Time
5:30 - IST 1942 Sep
5:30 1:00 IST 1945 Oct 15
5:30 - IST
A bit hard to read since this software compresses tabs and multiple spaces (Is there any way to create a table?) Kolkata use to be known as Calcutta. Until 1880, it was on LMT (5:53:28). Until 1941, it was the same time as the city of Howrah. In 1942, it went to Burma time (6:30), then to IST (India Standard Time). Thus, India (or at least Kolkata) was on 5:30 before GMT since 1942.
Looking at Pakistan:
Zone NAME GMTOFF RULES FORMAT [UNTIL]
Zone Asia/Karachi 4:28:12 - LMT 1907
5:30 - IST 1942 Sep
5:30 1:00 IST 1945 Oct 15
5:30 - IST 1951 Sep 30
5:00 - KART 1971 Mar 26 # Karachi Time
5:00 Pakistan PKT # Pakistan Time
Until 1907 Karachi was using local mean time. After that, it was using India Standard Time. In fact, it stayed on India Standard Time until March 26, 1971 when it went on PKT which is the same year East Pakistan became the independent country of Bangladesh.
So, Pakistan and India were using the same clock until 1971. After there was no more East Pakistan, it makes sense that Pakistan adopt 5-GMT since it centers nicely on their country, and there was no need to worry about time differences in a no longer existent eastern half.
Yes, Nepal is 45 minutes off the mark, not 40 minutes like Cecil’s column says. That puts them 15 minutes ahead of India. When we were in Nepal, the wife and I were told t was to emphasize that Nepal was separate from India, but that could be BS, dunno.
Quite a few years ago I was walking around The old observatory in New Deli, India and asked this very question of one of the museum guides. He explained that the Jantar Mantar( this collection of astronomical measuring devices was built in 1724 by Maharaja Jai Singh II of Jaipur, as he was given by Mughal emperor Muhammad Shah the task of revising the calendar and astronomical tables. They knew what time noon was.
Greenwich mean time was adopted across England about 150 years later, so the Indians do not see why today they should keep time to suit London time, in favor of their older and more accurate notion of noon in their capital.
That makes no sense unless the Indian observatory is at an exact odd multiple of 7.5° east of the observatory at Greenwich. And it also makes no sense unless pre-British India was well equipped with Morse telegraphs and steam railroads.
The answer is the simple answer that Cecil gave. India wanted to have a single time zone and the standard time zones basically cut India right down the middle.
Having spent time in both Bombay and Calcutta, I consider this a misfortune for Calcutta, where the sun rises and sets too early.
You think that’s bad, look at China which is four timezones wide, but uses Beijing time across the entire country. No wonder the people in Tibet are so up in arms, their day starts at what should be 4am in the morning.