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3 months. In our testing, we found that any distance longer than 250 pixels or so seemed like too much. This is our current approach to that situation.
Threads has been tested with FavePersonal, Twenty Ten, Twenty Eleven, Twenty Twelve and Twenty Thirteen (beta). We hope it will be compatible with most themes, but cannot guarantee compatibility with any specific theme.
Ask them in the support forums and we'll add them here as they are answered.