How does silentRenew and and useRefreshToken work in Angular auth oidc?

Question

The project I am currently working on has this configuration:

auth: {
 silentRenew: true,
 maxIdTokenIatOffsetAllowedInSeconds: 700,
 useRefreshToken: true,
 renewTimeBeforeTokenExpiresInSeconds: 60,
}

I think by setting silentRenew and useRefreshToken to true, it would automatically extend the session. But how do they actually work behind the scene?
I am currently trying to implement a function where a modal will pop up when the session time is 5 mins left.

How I was observing my session expire time:

1. After the user got the token, I call a check token method:
2. In the check token method, I basically just console.log the current time and expired time

    this.oidcSecurityService.isAuthenticated$.subscribe(() => {
                    this.token = this.oidcSecurityService.getToken();
                    this.checkTokenExpired(this.token);
                });

    checkTokenExpired( tokenId: String) {
        setInterval( () => {
            const currentTime = (new Date).getTime();
            const expireSessionTime = (JSON.parse(atob(tokenId.split('.')[1]))).exp * 1000;
            const exp= new Date(expireSessionTime);
            const cur = new Date(currentTime);
            console.log('cur', cur);
            console.log('exp', exp);
        }, 10000);
    }

However, after the session time expired, the session is still working and user can still interact with the App.
So I assume that the silentRenew and useRefresh token renew the session behind the scene. But when did it renew the session and how can I catch that so I can get the renewed session expire time?