They actually taught that Jesus arrived in 1874 and would become manifest in 1914 (40 years later). When that failed they danced around for a few years struggling to offer a few reasons for delay then revised their numbers saying they had actually said he would arrive in 1914. The 1874 actually was a spring off of the Millerites prediction of 1844. They added (30 years, Jesus time on earth). Its a tangled mess of pyramids and imaginary parallels. In the end when coincidently ww1 started kinda close to their 1914 date it cemented the prediction as fixed. They have been stuck with it since.
Your question about why they continue to do the sacraments is a valid one and reflects the arbitrary way they have timed expressions like "arrived" and "comes". Careful reading of old WT material showed me and my wife how often they casually shifted the timing of certain passages, I believe without awareness of doing it. I made the mistake of commenting that an statement i the WT was "new light" as they had applied a passage to a new time. I was told assertively it was not new or we would have been told it was new. I showed them the previous application and they told me to be quiet and not divisive. Its for good reason they no longer encourage having an extensive library.
In the end I imagine they need the sacraments to serve as a distinction between hierarchy and lay class.