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uses
  System.SysUtils, System.RegularExpressions;

function StrToTimeEx(const AValue: String): TTime;
var
  RegEx: TRegEx;
  Match: TMatch;
begin
  RegEx := TRegEx.Create('(([0-9]{1,2})?:)?([0-9]{1,2}):([0-9]{1,2})[\.,]([0-9]{1,3})');
  Match := RegEx.Match(AValue);
  if Match.Success and (Match.Length = Length(AValue)) then // check for length if the string should only be handled complete
    if Match.Groups[2].Length > 0 then // workaround for problem in TRegEx, Success is true though optional value is missing
      Result := EncodeTime(StrToInt(Match.Groups[2].Value), StrToInt(Match.Groups[3].Value), StrToInt(Match.Groups[4].Value),
        StrToInt(Match.Groups[5].Value))
    else
      Result := EncodeTime(0, StrToInt(Match.Groups[3].Value), StrToInt(Match.Groups[4].Value),
        StrToInt(Match.Groups[5].Value))
  else
    raise EConvertError.Create(Format('"%s" is no valid time!', [AValue]));
end;

// Test:
  ShowMessage(FormatDateTime('hh:nn:ss,zzz', StrToTimeEx('11:22.333')));