1 day is only 23h

Describe the bug

I recently noticed something strange using the following config:

object Service "check_by_selenium" {
    host_name = "***"
    check_command = "check_by_selenium"
    check_interval = 1d
    vars.selenium_project = "test"
    vars.selenium_testsuite = "icinga community forum"
    vars.selenium_with_images = true
}

My selenium icingaweb2 module writes to a database so I know the time the check is actually executed and the time between two checks is not 24h but only 23h

To Reproduce

1. create a service with intervall 24h or 86400
2. watch next execution

Screenshots

Selenium check:

Monitoring module:

IcingaDb module:

Your Environment

Include as many relevant details about the environment you experienced the problem in

• Version used (icinga2 --version): 2.14.3
• Operating System and version: Ubuntu 20.4
• Enabled features (icinga2 feature list):
• Icinga Web 2 version and modules (System - About): 2.12.2, icingadb 1.1.2
• Config validation (icinga2 daemon -C):
• If you run multiple Icinga 2 instances, the zones.conf file (or icinga2 object list --type Endpoint and icinga2 object list --type Zone) from all affected nodes.

Best Regards
Nicolas

Start by reproducing the reported behavior with a service configured with a 24-hour or 86400-second interval, then compare execution timestamps with the configured interval. Investigate the interval scheduling path in the Icinga 2 core; done means consecutive executions are separated by the configured duration, including around the reported environment and version.