Can I replicate same accounting records in more than one database?

Yes, replication of accounting is possible through Advanced RADIUS as well. You can create multiple accounting handlers in configuration file and specify these handlers in the realm being used. You must select REPLiCATiON policy for accounting.

Where does Advanced RADIUS stores accounting records by default and in what format?

By default, Advanced RADIUS writes accounting records in text file(s) in AcctDirectory. Format of these accounting files is similar to Livingston's accounting file.

How can I limit a user to login at night time (2100-0100) only?

in user's check items you should add an attribute named Time and specify its value to the time and day you want for this user's authentication.

For example, you want to restrict user Tom to login within these timings for all week days.

TomUser-Password = Tom, Time=Al2100-0900
Service-Type = Framed-User
Framed-IP-Address = 255.255.255.254
Framed-IP-Netmask = 255.255.255.255

This will restrict user Tom to login only within above timings and all days of the week.

How can I use authentication from one database while accounting from another?

# Line starting with '#' is a comment

# parameters of Realm
# Authentication Handler. See
AuthBy = db1_auth;

# Session Handler. See
Session = db2_session;

# Accounting Handler. See
Accounting = db2_acct;
# parameters of AuthBy db1_auth
BackStore = DB;
DBParams = db1_params;
AuthQuery = Select attribute-list from TableName where some-condition
# parameters of Session db2_session
BackStore = DB;
DBParams = db2_params;
# Query to perform insertion of session start records
# You can find following query samples from sample configuration files.
insertSession = RADIUS insert query;
DeleteSession = delete session query;
# Query to count active users'sessions
CountSession = session-count query;
# parameters of Accounting db2_acct
BackStore = DB;
DBParams = db2_params;
# Query to insert accounting stop record to sql table
insertAcct = RADIUS insert query;
# parameters of DBParams db1_params
# Driver name is the name of database driver
DriverName = sun.jdbc.odbc.JdbcOdbcDriver;
# Specify URL of the databse against the value of 'DBURL'
DBURL = jdbc:odbc:auth;
# Name of the user having previliges to access database.
UserName = admin;
# User's password to access database
UserPassword = admin;
# parameters of DBParams db2_params
# Driver name is the name of database driver
DriverName = sun.jdbc.odbc.JdbcOdbcDriver;
# Specify URL of the databse against the value of 'DBURL'
DBURL = jdbc:odbc:acct;
# Name of the user having previliges to access database.
UserName = admin;
# User's password to access database
UserPassword = admin;