Update Billing API Truncation Rules (#4571)

* update rule

* Update billing-api.mdx

---------

Co-authored-by: Brian MacDonald <brian.macdonald@temporal.io>

Author: mksample

docs/cloud/billing-and-usage/billing-api.mdx

@@ -51,7 +51,7 @@ For public preview, reports can be generated with hourly, daily and monthly gran
 
 Date ranges must use billing-month boundaries (MM/YYYY). 
 Requests may include the current billing month. 
-The data in finalized reports includes usage up to `current_time` \- 24 hours (rounded up to nearest hour).
+The data in finalized reports includes usage up to `current_time` \- 24 hours (rounded down to the granularity level).
 
 ## Rate limits and concurrency