You'll need to convert to epoch seconds or use an offset from the current time. For example: sched_api +3600 foo originate user/1000 &park
Will call user 1000 in 3600 seconds (1 hour) and park the call. (Obviously you'll send the call somewhere other than 'park')
If you want an absolute time then you'll need to convert to epoch seconds. Use 'strepoch' to convert a date/time string into epoch seconds. The 'strftime' displays the current date/time in the proper format:
freeswitch@internal> strftime 2012-05-29 12:40:22
By itself, 'strepoch' displays the current date/time in epoch seconds: freeswitch@internal> strepoch 1338320491
To get a specific date/time just feed it as an argument. 6PM tonight is this: freeswitch@internal> strepoch 2012-05-29 18:00:00 1338339600
Feed that into your sched_api: freeswitch@internal> sched_api 1338339600 foo originate user/1001 &park +OK Added: 10
2012-05-29 12:44:01.405063 [DEBUG] switch_scheduler.c:214 Added task 10 sched_api_function (foo) to run at 1338339600
And verify that task 10 is there: freeswitch@internal> show tasks task_id,task_desc,task_group,task_sql_manager,hostname 1,zrtp_cache_save,core,0,fs.debian 2,heartbeat,core,0,fs.debian 3,check_ip,core,0,fs.debian 4,limit_hash_cleanup,mod_hash,0,fs.debian 10,sched_api_function,foo,0,fs.debian
5 total.
freeswitch@internal>
And use 'sched_del' to remove it if you no longer need it: freeswitch@internal> sched_del 10 +OK Deleted: 1
Bonus feature: use 'expand' API to roll it all into a single command: freeswitch@internal> expand sched_api ${strepoch 2012-05-29 18:00:00} foo originate user/1001 &park +OK Added: 11
2012-05-29 12:48:11.785045 [DEBUG] switch_scheduler.c:214 Added task 11 sched_api_function (foo) to run at 1338339600
Please tinker away and let us know what you decide to do. You'll need something to talk to the FreeSWITCH event socket to send all these commands. Any ESL (event socket library) compatible language is a good choice. We have people who use Perl, Python, PHP, and Ruby all successfully, so any of those is a good choice.