Need to indicate timezone next to time but looks like some of the countries have same time zone for example Ireland and India share same "IST". How do we differentiate? Any help is appreciated. Thanks in advance
Rather than using the timzone's explicit name, you could use the UTC timezone system, or more specifically, UTC time offsets.
So for example, the UTC offset for India would be UTC+05:30.
The answer depends on the context of your user.
If we are talking about an American user base, then only the four main time zone abbreviations used in North America (ET, CT, MT, PT*) make sense. (Up to you if you want to include Newfoundland, Atlantic, Alaska and Hawaii-Aleutian, but even those you may want to write out.) Beyond that, either giving a written location (Irish time, Istanbul time) is most meaningful.
If you need a short form to fit your field, or if your users need to be able to calculate the time difference, then UTC+/-hh:mm is a good notation, but even then your average user will need to look up what UTC is, what their relative time to UTC is and figure out the difference.
Speaking of relative time, this may be another solution. If you are showing the date to an article or submission of some sort, rather than struggle give a specific date and time in a context your user understands, you could go with what most social media platforms use now and (for anything short-term) say "x minutes ago" or "y days ago"
(*You may have noticed I used ET instead of EST/EDT. In my experience, people get the difference between Standard and Daylight Saving time confused, and so unless it's necessary I recommend ommiting it and referring to just ET or "Eastern Time".)
If your site or app is internationalized and/or multilingual, your best bet is to use a localized version of Unicode's Common Locale Data Repository. Here is the time zone names and abbreviations to use in British English, for example.