I backtested it on my 5-minutes minidow data. I am on European Central Time so that "buying the close of 1555", which in turn means buying the open of 1600, really means 0955 am and 10 am EST:
Inputs: x(6), y(4), z(12);
{*** entries ***}
If time=1555 and c < c[x] Then Begin
buy this Bar at c;
value2=c;
End;
If time=1555 and c > c[x] Then Begin
sell this Bar at c;
value2=c;
End;
{*** exits ***}
exitlong at value2+y limit;
exitlong value2-z stop;
exitshort at value2-y limit;
exitshort value2+z stop;
----
I optimised x, y, z, to find out many interesting things.
"Z" likes to be given a high value, 10-20 ticks and even more, the higher it is the more profitable the system is. Not strange because that's the stoploss - it likes to be high. That's why when I try to trade with small stoplosses I end up losing more money than with larger ones. That would encourage me to have no stoplosses at all, but then sooner or later you get that one trade that wipes you out completely. At any rate, with a small stoploss as he asked to test, the system loses money, even if it had zero commissions.
"y", take profit, likes a smaller value, like 6-10 ticks, which would be half as many on the SP I suppose.
"x" is how many periods we have to go back to a value that's indicative of a later reversal at 10 am. It seems that we should go back to 9.30 rather than to just 5 minutes earlier to find the required higher value for longs, and lower for shorts, which we need to trigger a trade. But from 9.30 to 9.50 works.
If we make all these changes, higher stoploss, further "previous close"...the system becomes profitable, but not very profitable. It makes 800 dollars with 1 minidow in 6 months on the long trades, and it makes just 100 dollars with the short trades.
The good news is that if I reverse the "> previous close" condition, it makes less money, so it means the idea of a reversal at 10 am is not wrong, but it's not enough for a system, at least as far as my limited testing capabilities tell me. I mean the system you thought of, with a much larger stoploss than you said, seems to work, but not well enough to be used, since you risk too much money to make too little.