Q:

For flight planning must the forecast weather be above minima one hour before, after or at ETA? (EU-OPS)

Citing EU-OPS:

CAT.OP.MPA.185 Planning minima for IFR flights — aeroplanes
(a) Planning minima for a take-off alternate aerodrome

The operator shall only select an aerodrome as a take-off alternate aerodrome when the appropriate weather reports and/or
    forecasts indicate that, during a period commencing one hour before
    and ending one hour after the estimated time of arrival at the
    aerodrome, the weather conditions will be at or above the applicable
    landing minima specified in accordance with CAT.OP.MPA.110. The
    ceiling shall be taken into account when the only approach operations
    available are non-precision approaches (NPA) and/or circling
    operations. Any limitation related to OEI operations shall be taken
    into account.

(b) Planning minima for a destination aerodrome other than an isolated destination aerodrome

The operator shall only select the
    destination aerodrome when:

(1) the appropriate weather reports and/or
      forecasts indicate that, during a period commencing one hour before
      and ending one hour after the estimated time of arrival at the
      aerodrome, the weather conditions will be at or above the applicable
      planning minima as follows:

(i) RVR/visibility (VIS) specified in accordance with CAT.OP.MPA.110; and
(ii) for an NPA or a circling operation, the ceiling at or above MDH;

or
(2) two destination alternate aerodromes are selected.

(c) Planning minima for a destination alternate aerodrome, isolated aerodrome, fuel en-route alternate (fuel ERA) aerodrome, en-route alternate (ERA) aerodrome

The operator shall only select an
    aerodrome for one of these purposes when the appropriate weather
    reports and/or forecasts indicate that, during a period commencing one
    hour before and ending one hour after the estimated time of arrival at
    the aerodrome, the weather conditions will be at or above the planning
    minima in Table 1.

[...]

On the other hand:

CAT.OP.MPA.245 Meteorological conditions — all aircraft
(a) On IFR flights the commander shall only:

(1) commence take-off; or
(2) continue beyond the point from which a revised ATS flight plan
    applies in the event of inflight replanning, 

when information is
  available indicating that the expected weather conditions, at the time
  of arrival, at the destination and/or required alternate aerodrome(s)
  are at or above the planning minima.
(b) On IFR flights, the commander shall only continue towards the
  planned destination aerodrome when the latest information available
  indicates that, at the expected time of arrival, the weather
  conditions at the destination, or at least one destination alternate
  aerodrome, are at or above the applicable aerodrome operating minima.
(c) On VFR flights, the commander shall only commence take-off when
  the appropriate weather reports and/or forecasts indicate that the
  meteorological conditions along the part of the route to be flown
  under VFR will, at the appropriate time, be at or above the VFR limits
CAT.OP.MPA.246 Meteorological conditions — aeroplanes
In addition to CAT.OP.MPA.245, on IFR flights with aeroplanes, the commander shall only continue beyond:

(a) the decision point when using the reduced contingency fuel (RCF)
    procedure; 
or
(b) the pre-determined point when using the pre-determined point (PDP)
    procedure,

when information is available indicating that the expected
  weather conditions, at the time of arrival, at the destination and/or
  required alternate aerodrome(s) are at or above the applicable
  aerodrome operating minima.

So, should a commander of an operator's flight opt to commence a flight when the forecast at the ETA is above the minima, or the forecast needs to be above the minima for the period from one hour before the ETA till one hour after the ETA?

A:

Weather above planning minima one hour before and after ETA for flight planning and for determining alternate requirements (2 alternates vs 1).
Weather above planning minima at ETA for commencing flight. 
Weather above operating minima at ETA for continuing flight.

One way you can think of it: in the cockpit weather at ETA. In the briefing room weather one hour before and after.

