Your query should looks like:
PARAMETERS dt1 DATE, dt2 DATE;
select * from table where DataTime_Join1>#dt1# and DataTime_Join2<#dt2#
Then add parameters to command:
OleDbCommand command = new OleDbCommand(commandText, connection);
command.CommandText = "^^^above query^^^"
command.Parameters.Add("dt1", OleDbType.Date);
command.Parameters["dt1"].Value = time1;
command.Parameters.Add("dt2", OleDbType.Date);
command.Parameters["dt2"].Value = time2;