GetTimerManager just returns pointer to global TimerManager instance.

InitTimerManager explicitly initialize global TimerManager instance, which should be invoked before all timer creation behaviors.

NewAtScheduled returns scheduler from at expression.

NewCronScheduled returns scheduler from cron expression Classic style and new styles of cron expression are both supported: * Classic: `Seconds Minutes Hours Day_of_month Month Day_of_week` * New: `Seconds Minutes Hours Day_of_month Month Day_of_week Year(optional) Timezone(optional)` For timezone specification, two formats are supported: * Complete name in TZ database, e.g., Asia/Shanghai, America/Los_Angeles * GMT offset (no leading zero in hour), e.g., GMT+8:00, GMT-6:00 * Some fixed and unambiguous abbreviation names of timezone, namely: + GMT + UTC.

NewRateScheduled returns scheduler from rate() expression.

GMT+13:00/GMT+14:00 do exist, even GMT+13:45.

CronScheduled provides nextRun() interface for cron expression.