Approximate length of is 10 bars (10 hours). From the first trend shown up, there will be fluctuation until approximately 10 bars. After that it could go short again or up.
EDIT: 4:30 Server Time (Metatrader) / 1:30 (TradingView): From the first time trend shown up, there will be fluctuation until approximately 5-7 bars (5-7 hours), after that it could go short again or up.
Latest chart for EURUSD MAY 15.2015/16:30 (Metatrader)/13:30 (TradingView). As previously analysed, approximately until 5-7 bars.
Good Luck :)