TM1 chore scheduling is frequency based, i.e. it will run and try to pull data after a predefined period of time regardless of the availability of the data at the source. Unfortunately it can be a hit or miss and it can even become a maintenance issue when Daylight Saving Time come into play.
Ideally you would need to import or get the data pushed to TM1 as soon as it is available. The following article shows one way of achieving that goal with an iSeries as the source...

prerequesites on the TM1 server:

• Mike Cowie's TIExecute
• iSeries Client Access components (iSeries Access for Windows Remote Command service)

Procedure to follow

1. Drop TM1ChoreExecute, TM1ProcessExecute, associated files and the 32bit TM1 API dlls in a folder on the TM1 server (see readme in the zip for details)
2. Start iSeries Access for Windows Remote Command on the TM1 server, set as automatic and select a user that can execute the TM1ChoreExecute
3. In client access setup: set remote incoming command "run as system" + "generic security"
4. On your iSeries, add the following command after all your queries/extracts:

RUNRMTCMD CMD('start D:\path\to\TM1ChoreExecute AdminServer TM1Server UserID Password ChoreName') RMTLOCNAME('10.xx.x.xx' *IP) WAITTIME(10)
10.xx.x.xx IP of your TM1 server
D:\path\to path where the TM1ChoreExecute is stored
AdminServer name of machine running the Admin Server service on your network.
TM1Server visible name of your TM1 Server (not the machine name of the machine running TM1.
UserID TM1 user ID with credentials to execute the chore.
Password TM1 user ID's password to the TM1 Server.
ChoreName name of requested chore to be run to load data from the iSeries.

You should consider setting a user/pass to restrict access to the iSeries remote service and avoid abuse.
But ideally an equivalent of TM1ChoreExecute should be compiled and executed directly from the iSeries.