The Challenge
All date and time values in doForms are stored in the Universal Time (UTC) format which is also known as Greenwich Mean Time (GMT). This is a standard approach that allows for the precise recording of any moment in time, regardless of which time zone the user was in when they recorded the time.
Most businesses, of course, need to see time information in the local time zone so the best practice for applications is to store date and time values in UTC and only convert them to local time before display.
The doForms web site follows this practice and allows you to set a time zone under Account and then Time Zone Settings:
Note that this only changes the way time is displayed on the web site. All time values are still stored in UTC.
If your system / application follows this practice, then no changes to the doForms data will be necessary. If however, your application requires local time, then some additional work is required...
Time Zones and Offset
To convert from UTC time to a local time zone, you first need to know how many hours or minutes to add or subtract from the UTC time. This is commonly called an Offset and is often specified as part of a time zone description, e.g. "Central Time (U.S. and Canada) GMT-6:00". The GMT-6:00 indicates that you subtract 6 hours from GMT/UTC to convert to the Eastern time zone. If you are unsure what your current time zone offset is, try taking a look at this map of the current time around the world.
Note that the offset for a time zone will change during Daylight Savings Time. For instance, the offset for Central Time (U.S. and Canada) changes from -6:00 to -5:00 during DST.
Each time a form is completed on a device, doForms captures the current time zone offset (in minutes) of the device and stores it in a field called timezone:
Converting To Local Time
- Convert all submission times to the device time
To convert all submission time values to the device timezone, select the "Convert submission times to local" under Tools | Options | Jobs | Submission. - Use the device timezone offset
To convert individual date/time or time fields to the local time of the device, select the Local Date Time data type:
If the "Convert submission times to local" option is selected then this configuration does not change the time value. - Specify a timezone offset
To convert individual date/time or time fields to a timezone other than the device, choose the Local Date Time data type and enter the field and offset separated by a coma:
This will convert all values to the same time zone by adding -300 minutes. Note that the Name of the field should be entered in the Name column.
This configuration will override the "Convert submission times to local" option.
- Use a special field
The special fields Date_Created_Local and Date_Received_Local contain the local (device specific) values of the Date_Created and Date_Received fields.
Note that using the timezone offset captured from the device will convert each time value to the time zone of the individual user. If you have users in multiple time zones this can lead to confusion. For instance, consider the example of a user named Jim in the Eastern (U.S. and Canada) time zone who enters a time of 10:00 AM and a user named Bob in the Central (U.S. and Canda) time zone who enters a time of 9:05 AM. Later, when someone views this data in another application, they might suppose that the event entered by Jim at 10:00 AM occurred after the event entered by Bob at 9:05 AM, when the reverse is actually true.
Converting After Export
To use your back end system (instead of Sync & Save) to convert to local time, you will need both the timezone offset and your time value(s). In the example below, the Time_question and timezone values are exported to two separate fields:
Once you have the Offset value for a submission, you will need to convert each time value to the correct local time. Below are examples for some output options:
Excel
If you have a UTC time value in A1 and the offset (in minutes) in B1, the formula in C1 will convert to local time. First we have to convert the time to a date (we choose 1/1/2000 arbitrarily) and then we add the number of days represented by the offset (minutes divided by number of minutes in 1 day) to convert to local time.
If you have a UTC date and time value, then the conversion to a date is not necessary and the equation would just be A1 + B1/1400.
Access
If you have a UTC time or date value in a Date/Time field in a table called "s" the following query expression will convert it to local time:
LocalTime: DateAdd("n",[s].[timezone],[Time_question])
Note that if you are converting a time value, this will display with a date value as well (e.g. 7/8/2013 9:30:40 PM) because the Access field is a Date/Time format. The date portion is not the date that the time was entered, instead it is the date the record was inserted into Access. If you want to eliminate this date portion, use the following query expression:
LocalTime: Format(DateAdd("n",[s].[timezone],[Time_question]),"hh:nn:ss ampm")
Sql Server
If you have a UTC time or date value you can convert to a local time using the query expression above.
Note that the if you just have a time value, the date portion of the value comes from the default of Jan 1 1900. If you want to only display the time portion of the value, use the following expression:
SELECT SUBSTRING(CONVERT(varchar, DATEADD(N, timezone, Time_question), 0), 12, 8) AS LocalTime FROM t
Result: "9:30PM"
Or if you prefer the 24 hour clock, use:
SELECT CONVERT(varchar, DATEADD(N, timezone, Time_question), 0) AS LocalTime FROM t
Result: "21:30:40:000"