For most TMA situations there has to be a significant difference in bearing lines in order for it to be helpful in generating a solution, so 2 minutes is about the minimum in most sonar tracking situations for the additional lines to be helpful in determining a solution.
The presence of more lines, if they are all very close in bearing and time is not that much more helpful than a line every 2 minutes, actually I've found that more lines can make it more difficult in generating a solution, like when I mark the same ESW contact 50 times in a minute, it can make the TMA process very hairy.
