For information on dataset creation / last modification date, check the Contents procedure, or the SASHELP.VTABLE view.
For comparing datasets, use the Compare procedure.
To make SAS wait, you can use the SLEEP function within a Data step.
For conditionnal executing of SAS programs, see what you can do with macro language.
here is some sample (untested!) code you can start with. Have a look in doc for PROC COMPARE and SYSINFO for details.
About the rechecking, I suggest that you use a scheduling tool for that, such as cron in UNIX.
dsid = open('libname.table');
updated_dt = attrn(dsid, 'MODTE');
if "&SYSDATE9"D eq datepart(updated_dt) the call symput('UPDATED','Y');
else call symput('UPDATED','N');