Those are just custom fields they will not behave like System Time Tracking field.
Unfortunately there is no option in JIRA to add custom Time Tracking field. There is feature request for that with atlassian you can vote on this ticket - https://jira.atlassian.com/browse/JRA-12920
Also what you are looking for might be available through plugin and one such Plugin for Time Tracking is Tempo - http://www.tempoplugin.com/products/tempo-timesheets/
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