We've noticed that "time_zone" and "utc_offset" fields are "null" for some profiles. See examples bellow...
1)
https://api.twitter.com/1.1/users/show.json?user_id=1246330681
https://apigee.com//snapshot/twitter?snapId=apigee-console-snapshots-1380603600000_339ba752-f7e9-40b9-8d57-bdc29e23d70b
2)
https://api.twitter.com/1.1/users/lookup.json?user_id=1246330681
https://apigee.com//snapshot/twitter?snapId=apigee-console-snapshots-1380603600000_ddc39a11-1e74-4930-afd4-34fa9b50f187
Screenshots: http://cl.ly/image/3I1m2d2R3Z0o, http://cl.ly/image/2i3m1T1g3a1G.
We are able to provide a list of hundreds of profiles like this one. It's weird, because we thought that setting a timezone is mandatory and thus it should not be returned as null for any profile.
Thank you for investigating this.