I remember there was a bug where Tasks did not finish but run endlessly until they are manually stopped when there is no end time/date given. This was resolved in ePO 5.1.3 and I can confirm the fix is working, at least for us.
It would be terrific if you could provide your ePO Version and have a look to the "known issues" für your Version: McAfee KnowledgeBase - REDIRECTED - ePolicy Orchestrator 5.1 Known Issues
Nevertheless: If all your managed or to-be-managed Systems are within ONE Group you can easily create an Installtask for only this Group the Clients are in (or you could create an installgroup with specific sub-Groups). Besides it could be useful to open a SR (request for Information) and ask for best practices which come handy to your Environment and in this matter.
I am sorry for my english but I hope it is at least understandable.