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Abstract: To produce short X-ray pulses for SwissFEL 1 [1] FEL: Free Electron Laser; SITF: SwissFEL Injector Test Facility; OPCPA: Optical Parametric Chirped Pulse Amplifier; PLL: Phase Locked Loop. , it is necessary to compress the electron bunches by a factor of 300, down to sub-fs for the attosecond operational modes. To achieve stable FEL output accurate timing of the initial electron injection at the main linear accelerator is necessary. Tolerance studies show, that to reach the final performance goals, less than 40fs relative rms jitter is required from the electron gun, relative to the reference. Here we present independent residual RF phase noise measurements of the laser oscillators, showing an exceptional ~30fs integrated rms jitter. Moreover timing studies at the SwissFEL Injector Test Facility, based on charge detection at the sharp rising edge of the Schottky-scan were performed allowing for systematic correlation studies and showing a residual jitter of ~150fs at 10Hz from the pulsed laser system and beam transport respect to the reference. For future development, available relative jitter measurement techniques for pulsed laser systems will be reviewed and their applicability for laser arrival time monitoring and feedback for FEL applications will be discussed. [Copyright &y& Elsevier]