Thanks a lot for your answer.
So Please confirm my understanding : To run the current scheduled  build on every (scheduled) time ,I need to :
1). uncheck both the options OR
2). only "Build only if there are changes accepted" option(But in this case Build is not   triggered). I do not know if I need to delete previous RTC build.
3). Any other configuration in the build definition ,I am missing which supports point 2?

With above comments please find some additional info so that you can suggest me :
1). We created only one BuildDefinition(by copying from existing BD) and then un checked the "Build only if there are changes accepted" option.
2). BD's "scheduledBuild" property is set to "true".
3). This BD use to create  3 ears and 20 jar files.
4). This Build is triggered(on scheduled time) only if some code is checked in ingoing of point 1 else build will not be triggered.
5).I have checked the log file name as "002 - BD Scan" and found 3 entries team_scm_acceptBeforeFetch and team_scm_buildOnlyIfChanges.
First entry says(But my BD the second option is unchecked) :
team_scm_acceptBeforeFetch=true
team_scm_buildOnlyIfChanges=true

Last 2 entries says :
team_scm_acceptBeforeFetch=true
team_scm_buildOnlyIfChanges=false
So ,Do I need to set team_scm_buildOnlyIfChanges to false manually in jazzSourceControl Tab? Please guide me
 

 You don't need to uncheck both.  "Build only if there are changes accepted" matches up to the property team_scm_buildOnlyIfChanges property.  It allows the build to run everytime.  The other option "Accept latest changes before building" just accepts the latest into the build workspace before the build, making sure that you are always running builds from latest.  So it is likely you want to keep that option on.

Yes ,I got your point. But in my BuildDefinition I have set  "Build only if there are changes accepted" false. And this BuildDefinition is associated to BuildForge project. So DO I also need to set team_scm_buildOnlyIfChanges false in that project?

 The variables in BF should be overridden by the values coming in from RTC.  You can change that value, but the value in BF should never 'stick'.  It should always be the value of the variable in RTC.