Policies will only evaluate a complete day and the previous calendar day does not have a full 24 hours worth of data available. 

The policies for AWS and Azure cost and usage information will compare *3 days prior to 2 days prior* as we assume partial data for yesterday.  Cost policies will NOT be evaluating the prior day of partial data.  It will skip over that day.  For example, if today is February 7th and a policy is designed to evaluate on a daily cost increase, the platform will compare the first two days of full data.  Due to the previous day (Feb 6th) having partial data, the policy will evaluate metrics from February 5th and February 4th.  The usual caveats apply (like having to have costs for all accounts in order for the policy to evaluate).