I understood your requirement.
I have 2+ years of Experience in Embedded Software/Firmware development. I have been worked on the developing BSP and low lever Device driver for our custom boards based on ARM, AVR, 8051, MSP430. I can complete the project within the specified period of time.
You haven't specified any what kind of project to be done with the 8051/AVR. But your project can be done within one week time for any board/microcontroller. It would be more helpful to decide the time, compilers and tools required if you specify the project.
If it is simply a small piece of code to do some tasks with peripheral functionality (UART, I2C, timers, SPI etc.,) that can be done within the time frame of 3 working days.
Thanks & Regards,
Balasubramanyam Rangineni