Assuming that you are using a master snapshot:
First guess is that your firmware has been compiled with the older musl C library 1.1.24 instead of the curent 1.2.2. The musl version upgrade in September changed the internal time handling from 32bit to 64bit even in the 32bit targets (like mipsel24).
You likely need to sysupgrade your firmware to the current version, and then install openssl compiled with the same libraries.