Short answer

You may experience delays in order placement when the market opens due to two main reasons:

Exchange capacity limitations: When the number of orders exceeds the maximum number the exchange can handle, the exchange lines become congested. Your order can take up to a few seconds to process during these peak periods.

Broker order queue: Every broker connects to exchanges through leased lines with a specific order per second capacity. When this capacity limit is reached, your orders join a queue and can take a few seconds to process.

These delays are temporary and typically occur only during high-volume trading periods at market opening.