As an Network Engineer, I want uptime and downtime values to be calculated based on the selected time period (both in web interface tabs like "30 days" and API calls), so that I can get accurate availability metrics for specific reporting periods instead of misleading lifetime values that include the entire sensor history since creation.

Currently, PRTG calculates uptime/downtime values from sensor creation time regardless of the requested time period, which creates misleading availability statistics when users need period-specific reports.