If you put an argument with a ridiculous timer it will throw an out of range exception. 
Full error below.

/mute <steamid> 12312312123d "weird"
Gets you the error below.

Failed to call hook 'CmdMute' on plugin 'BetterChatMute v1.2.1' (ArgumentOutOfRangeException: TimeSpan overflowed because the duration is too long.)
  at System.TimeSpan..ctor (System.Int32 days, System.Int32 hours, System.Int32 minutes, System.Int32 seconds, System.Int32 milliseconds) [0x00051] in <eae584ce26bc40229c1b1aa476bfa589>:0
  at System.TimeSpan..ctor (System.Int32 days, System.Int32 hours, System.Int32 minutes, System.Int32 seconds) [0x00000] in <eae584ce26bc40229c1b1aa476bfa589>:0
  at Oxide.Plugins.BetterChatMute.TryParseTimeSpan (System.String source, System.Nullable`1[System.TimeSpan]& timeSpan) [0x001a5] in <a23add852bd8436ba23078546ebb3890>:0
  at Oxide.Plugins.BetterChatMute.CmdMute (Oxide.Core.Libraries.Covalence.IPlayer player, System.String cmd, System.String[] args) [0x00050] in <a23add852bd8436ba23078546ebb3890>:0
  at Oxide.Plugins.BetterChatMute.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0024b] in <a23add852bd8436ba23078546ebb3890>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <60c318df79ed41688ea59335e48d61ad>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <9882f28dc2204b4dba514a9ad18f5042>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <9882f28dc2204b4dba514a9ad18f5042>:0