Oribi LBR20 Failover delay to 4G

Hi

I have a Fibre (FTTC) connection with a 4G failover set up on my Orbi LBR20 4G Router (as my fibre connection is unstable) however when the fibre connection disconnects it can take up to 3 minutes for the failover to switch to 4G. please advise how and where i can change the setting this so the switch over is seamless and i do not lose any connection time as this is critical for my business

Many thanks