Crontab backup scheduling

Dear experts,

I have all these files at this location : /retekdb/oracle/oradata/simdb

I want all these files to be backed up through crontab at : /retekdb/backup/simdb 

Note: in tar.gz format with date example : databasename_date.tar.gz

I want cold back everyday at 6:30 am and hot backup everyday at 4 pm.  How to do it ? Please help me out. 

[dbuser@dba2 simdb]$ pwd

/retekdb/backup/simdb

 [dbuser@dba2 simdb]$ pwd

/retekdb/oracle/oradata/simdb

[dbuser@dba2 simdb]$ ll

total 6588860

-rw-r----- 1 dbuser dba   9748480 Dec 14 04:41 control01.ctl

-rw-r----- 1 dbuser dba   9748480 Dec 14 04:41 control02.ctl

-rw-r----- 1 dbuser dba  52436992 Dec 14 04:35 lob_data01.dbf