Estimations should be smart, not hard
Regardless if you are estimating in hours or story points, no individual task should take up more than 16 hours of work (with story points the upper limit may be 13-20). The reasoning behind this is that estimating work items that are larger lowers the degree of confidence, it being key for items that reside at the top of the backlog. When an estimation is above the presented threshold, it is an indication that the task needs to be broken down into smaller items and re-estimate.
When estimating backlog items that are lower in priority, estimations should be approximate. There is no need to spend more time estimating this work, as requirements may change as well as the application that the team is working on. It is still important to produce estimations for these, lower priority items, because they help the product owner prioritize the product road map.