When using the offset parameter:
You’re limited to 1,700 individual followers from either side of a channel’s follower list.
Twitch API documentation reference
Here’s an example list of calls to make:
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=100
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=200
...
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=1400
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=1500
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=1600
Only goes to offset 1600 with a limit of 100. And then in ascending order:
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&direction=ASC
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=100&direction=ASC
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=200&direction=ASC
...
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=1400&direction=ASC
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=1500&direction=ASC
https://api.twitch.tv/kraken/channels/CHANNEL_NAME/follows?limit=100&offset=1600&direction=ASC
So that’s something like 18200 calls. If each call is called consecutively and takes 1 second, it would take a little over 5 hours. At a more realistic 132ms per call, it could take 40 minutes.
Edit: Use the cursor param instead.