hmmm, the best entry has to be at the TOP or BOTTOM of the price for the instrument in question, now to get in at the absolute of the two is impossible, but i'd say you can dilute the top and bottom into top zones and bottom zones, the zones can appear immediate or drawn out depending on volatility,price action and volume,time of day.these levels these give good risk/reward opportunities.
now there is a lot of comment on trying to pick tops and bottoms doomed to failure etc and i'd agree if you are trying to get in at the absolute of the two, i'd say thats pure chance if you do, however entry at top zones and bottom zones is a skill that can be aquired or a trading method/plan that by the very nature of risk reward opportunity warrants investigation as a possible entry method for a trader to utilise.
A point to consider is also time of day, volatility,volume,price action, therefore greatest opportunity is at the first 90 mins and the last 90 mins of the trading period (stock index trading)
but a lot depends on so much else, an individuals timeframe, the objectives etc...
havn't looked at forex re volumes,volatility etc maybe someone else who studies forex can comment on time of opportunity relating to these markets.
jd.