Geocodio can return the timezone for any US or Canadian address or latitude/longitude point. You can upload a spreadsheet of addresses or coordinates, or use our API.
To get that information, just select "Timezones" in Step 3 of the upload process. You can see the API documentation on adding timezones to address or coordinates here.
You can download an example of the results when you add timezones to addresses here and to latitude/longitude coordinates here.
Requests are billed as geocode + ACS Social info (i.e., two lookups). For example, if you have 100 addresses that you want Veteran and Education information for, that would count as 200 lookups.
You can calculate how much this will cost you and how long it will take here.