ICAO PANS-ATM says
4.4.2.1.2 In the event of a delay of 30 minutes in excess of the estimated off-block time for a controlled flight or a delay of one hour for an uncontrolled flight for which a flight plan has been submitted, the flight plan should be amended or a new flight plan submitted and the old flight plan cancelled, whichever is applicable.
It offers no guidance on departing early, though it does say elsewhere (11.4.2.2.2.5) that:
transmission of the FPL message may be withheld until one hour before the estimated off-block time, provided that this will permit each ATS unit concerned to receive the information at least 30 minutes before the time at which the aircraft is estimated to enter its area of responsibility.
This would imply that departing more than 30 mins early might break the system.
The IFPS User's Manual, which applies to IFR FPLs in Europe (and hence does not answer your question), says:
Any changes of more than 15 minutes to the EOBT of a filed flight plan shall be communicated to the IFPS. The IFPS shall not accept negative delays: should the EOBT of a flight need to be changed to an earlier time that flight must be cancelled and re-filed with the earlier EOBT.
Note Although it is not a requirement to update the EOBT of a non-ATFM-regulated flight where the change is not more than 15 minutes, it is recommended to make such an update to the flight plan held by the IFPS.