Your question is a bit broad. Hardware (HW) could mean full custom ASIC / FPGA development, assembler-programmed DSPs, or "only" a typical embedded system based on off-the-shelf microprocessors/microcontrollers/SoC etc. (of course a SoC might also contain a DSP that you might want to program....).
For high sale quantities, making it an ASIC is not uncommon.
But for a 2 month project I expect it to be based on some microcontroller:
In any case, you should stress the hardware team to give you a prototype you can start testing your code before the absolute deadline - this just might consist of a generic development board, as some people have mentioned already, but in my opinion it is their job to provide the right one to you, and potentially also some required/similar peripherals for testing.
Simulators are also possible to some extent, but you still might need to characterize some real world sensors / data you might get. Here the hardware team also needs to at least assist you.
Other than that, the software design can be done already and all high level modules can get (and should be) implemented and unit-tested without the real hardware.
Ideally, you will also define an API together with the hardware team, and they will provide you with the lowest level functions, so any change they do on the hardware side there (e.g. simply redefining which port pins they use), will be not always be critical to you.
In all cases, communication is key.