The ARES linac at DESY aims at producing and characterizing ultrashort electron bunches for cutting-edge applications (e.g. advanced and compact longitudinal diagnostics development, advanced and compact accelerating structures test, FLASH radiotherapy, etc.). The targeted properties (100-150 MeV, down to sub-pC charge and sub-fs duration) make the characterization of the bunch duration a challenge on its own. A first measurement of the bunch duration on ARES, based on a traveling wave structure phase scan, was performed in spring 2021. Resolution-limited durations down to 50 fs rms for bunches compressed by velocity bunching were recorded. Two X-band transverse deflecting structures with variable streaking direction (PolariX type) will be commissioned end 2021 or beginning 2022 and will enable fully characterizing the ARES bunches with down to sub-fs resolution.