How to specify granularity for the Access log Timestamp field to display access log entries using Views?
Maybe the Views Date Format SQL module is what you're looking for. Here are some details (from its project page):

The Views Date Format SQL module allows to format date fields using SQL. This enables group aggregation for date fields using the choosen granularity.
The core functionality is to remove the date formatting from render() and put it in query(). I.e. format date values using SQL's DATE_FORMAT rather than PHP's format_date. This is achieved by assigning a new default handler to node 'created' and 'changed' date fields. This handler extends and overrides views's build in views_handler_field_date.
The UI is completely unobtrusive, only a single checkbox &quot;Use SQL to format dates&quot; is added to the handler configuration popup.

As an illustration, and/or to better understand the challenge here, you may want to look at Graph node input over time (support date formatting on a continuous axis) also. Comment #3 of that issue states: 'The trouble here is that neither Views nor Date modules provide aggregation options for date-based fields.'.