EP J171159.4−333253 is a new neutron star low-mass X-ray binary discovered in outburst by the Einstein Probe (EP) on 2025 June 23, exhibiting clocked type I X-ray bursts, eclipses, and dips. In this paper, we report on the results of the X-ray spectral and timing analyses for EP J171159.4−333253 using data collected by EP and NuSTAR during the first 21 days of the outburst. The X-ray burst recurrence time can be characterized over a subset of nine bursts spanning 1.6 days around the NuSTAR observation, and the result is trec = 8196 ± 177 s, with indications of a possible decreasing trend. From the X-ray eclipse events, the binary orbital period and the eclipse duration are estimated to be Porb = 6.48301 ± 0.00003 hr and D⋆,X=1245.5−6.5+6.9 s, respectively. These enable an estimate of the mass and radius of the companion star and the binary inclination, which are M2 ≍ 0.6─0.8 M⊙, R2 ≍ 0.7─0.8 R⊙, and i ≍ 73°─75°, respectively. We also report on joint ULTRACAM and EP observations on 2025 July 21─22, detecting the source optical counterpart and covering an eclipse in both X-ray and optical bands. The optical eclipse is wavelength dependent and broader than in X-rays, indicating that part of the optical emission arises from an extended region in the accretion flow. Despite a moderate variation in the source flux, the properties of the persistent X-ray emission are typical of a hard spectral state. We further evaluated the ratio of the accretion energy to the thermonuclear energy to be 120─130, implying helium bursts with the accreted hydrogen being depleted in between bursts.