Using the 2018-4-16 06:45 low would have been valid and depending on how tight your stop was you would most likely have been stopped out. This false breakout is quite common with triangles and in my opinion gives a bit more conformation that the breakout will be to the upside. After being stopped out I would have added a new trend line connecting the new low, and waited to see what happened next. There is 3 outcomes I would look for,
1. the price will continue lower, in which case my analysis was wrong and it would be too late to enter for this set up.
2. prices move a bit higher and finds resistance from the 2018-4-16 06:45 trend line and then continue lower. I would probably take a short position if we got back below 7.45 am low and would target the origin of the lower triangle line.
3. Prices move back up above the 2018-4-16 06:45 trend line, indicating a possible false breakout and we should move higher, which is what happened.
There is no way to be sure what is going to happen next when trading, all we can do is try and look at all possible outcomes and position ourselves as best we can to take advantage of them should they move in our favour. We will inevitably be wrong but If good risk management is used and stops are positioned correctly, profits should out weigh losses.