The time resolution (TR) is one of the most important characteristic of a detector. The particular case of a scintillator, the collection of light also is important, it depends of the sensitive area of the photo-sensor (Scorer). Normally, the Scorer of Photomultipliers Tubes (PMTs) is greater than the Scorer of Silicon Photomultipliers (SiPMs). Other differences are the voltage of operation, their size and cost, in some cases, the large size of PMTs can be difficult to place, if small space is required, in which case, it is preferable to use SiPMs. The value of TR also depends of the size and geometry of thescintillator, number of photo-sensors and the electronic part.In this work, we study the mean optical photon arrival time distribution (AT) to a Scorer from a SiPM of 6X6 mm2. We define the variation of AT as the intrinsic time resolution (ITR). In Geant4, we simulated two different geometries: square and hexagonal, for a BC-404 plastic scintillator coupled to one Scorer. The sources simulated were Sr90, Co60, Cs137, Na22 and μ- of 1 GeV. It is shown that AT and ITR depends of the geometry and size of the plastic scintillator, the location of the Scorer, the incident particle and its energy. Then, the ITR and therefore the TR is not a constant for a detector. Finally, we show the relation between AT and the deposited energy by the particle incident, which are related in the experiment to the response time event of the detector and the deposited charge by the incident particle, respectively.