Trade execution time

How much time should it take for a trade to execute? My strategy involves posting orders twice daily – at open and again at close. These are all major ETF’s

When I look at real online brokers (Scottrade, Fidelity, Scwab as a sample), they claim typical execution times of 1 second or less.

Here, opening trades usually take 1-3 minutes to execute. The orders are all placed 1 hr+ before opening.

Similarly, at close I have been parking the orders to execute at 3:58 because it takes a few minutes for he orders to typically be placed. And yesterday I missed a good trade because the ordered did not get placed within the final two minutes.

* Should I be parking the orders to leave 3+ minutes to ensure they are executed? (But I would prefer getting a price as close as possible to the open/close price).

* Is there a way to have the orders credited at whatever the opening or closing value is?

* For that matter, is there a real life way of getting an order credited at the opening or closing price? Would an order parked until 3:59:58 still get filled (remember these are major ETFs with large volume) and hence effectively be at the closing price?