I asked support about this 5 minute freeze. Below is their answer:
@LMAX support wrote:
“We close for 5 minutes each day to perform system maintenance, so that we can provide a better services.”
That should not be related with swaps though. Midnight EA opens trades around 10-11 PM at night. You will experience swaps if a trade is opened and not closed before midnight. If LMAX close everything for 5 minutes, i guess EA won’t trade anyway.