Delay for batch get symbol bars

I realized when I try to batch get 300 symbols, it took 2mins, which means the data
is delayed by 2mins?

So I switched back to get single symbol at a time, but alpaca keeps not getting
candles every 10 symbol after 5mins. I am not reaching the limit 1000api call/min.

BTW, some symbols are invalid. But how do we solve the delay problem for batch get?