Is there a way to get what month it is in Eastern Time?

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#1

You can write your topic however you want, but you need to answer these questions:

  1. What do you want to achieve?

I want to make a script that says what the month is in Eastern Time, for example it would be 12 for December.

  1. What is the issue?

The issue is that os.date only gives the time in UTC, and even if I subtract five hours that wont work for daylight savings time.

  1. What solutions have you tried so far?

I have tried using os.date but it doesn’t seem to work for time zones, I have also thought about using HTTPService but I would prefer to avoid using it because it is unreliable.

#2

The second argument of os.date is the time in seconds since the UNIX Epoch in which os.date should work off of. If you do not specify this argument, it defaults to the value of os.time.

local DATE_FORM = "%d/%d/%d"
local DATE_0 = os.date("!*t", 0)

print(DATE_FORM:format(DATE_0.day, DATE_0.month, DATE_0.year)) -- 1/1/1970

So, we’re going to use this argument to our advantage. Work in UTC time so that you can ensure a reasonable time, since the returned time isn’t exactly consistent across servers. Now remember that timezones are based on UTC as an offset of it.

Recall what EST is in terms of UTC: UTC-5. Eastern Standard Time (EST, UTC-5) is 5 hours behind Coordinated Universal Time (UTC). 5 hours is 18000 seconds (3600 seconds in an hour * 5 hours). This will be our offset from the current time.

local EST_SECONDS = os.time() - 18000

os.time is fetched as the number of seconds since the UNIX Epoch which is January 1st, 1970, in terms of UTC. So we offset it 5 hours back. This will serve as our time value. Now all that’s left is to plug it right into os.date which will send us back a dictionary of information about the given time.

local EST_SECONDS = os.time() - 18000 -- or os.time() - (3600*5)
local EST_DATE = os.date("!*t", EST_SECONDS)

local EST_MONTH = EST_DATE.month
print(EST_MONTH) -- 12

And there you are. The date in EST.

To summarise, here are the key concepts to take away:

  • The os library works in UTC unless able to specify otherwise (*t for os.date).
  • All timezones are an offset of UTC forward or backward by some hours
  • You must convert the hour offset into seconds to work with os.time properly
  • With the number you get above, add or subtract it from os.time to get the seconds in a certain timezone (for EST, it’s back 5 hours, so take away 5 hours in seconds from os.time)
  • Plug the number of seconds into the second argument of os.date so that it will form a date table based off of the seconds given

Fun fact: You can reverse this operation too. os.time accepts a date table argument (not documented), so if you know the exact information of these dates, you can retrieve the value of os.time for a specific date as well.

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Timezones In Scripting
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#3

Thanks but I didn’t say EST, I said Eastern Time, which means EST and EDT (Eastern Daylight Time), and while EST is UTC - 5:00, EDT is UTC - 4:00, so that code wont work during daylight savings time.

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#4

The date table comes with isdst. You can use this to determine the proper offset, either using 4 hours or 5. Simply change the offset and recalculate the time offset based off of this boolean.

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#5

The problem with isdst is that it only works if you use local time and not UTC time, and it always returns false regardless of if it’s daylight savings time or not because UTC doesn’t have daylight savings time (I tested this a few months ago when it was daylight savings time).

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#6

Fair enough. I can’t think of any other native way to do this then, I apologise. The only native method for working with real time is through the os library. If these kinds of time offsets don’t work for you, then trying to do this in-platform is bust (there may be weird workarounds that I haven’t covered though?) and you’ll have to look externally.

There’s a class currently in development, DateTime, but I’m not sure if it’ll be the solution to your problem when it’s pushed to production. That’s just from me looking at the DateTimeKind enum and the High-Level Platform Roadmap, so I have no legitimate citation right now about it.

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