Just to follow up here and document things for anybody who is building their own AmbaSat from schematics, it turns out that the ATmega328P provided in the kit has the following fuse settings:
(E:FE, H:D6, L:62). Those settings cause the ATmega328P to ignore the external resonator that you do solder on the board and use the internal clock with a divider of 8, make the code run at 1 MHz. Presumably this is done to minimize power needs since we are running off solar panels while in space, which is good. The incidence angle that the solar panels will catch sunlight at could vary greatly, which means the power output would vary greatly. Minimizing power needs greatly increases the operating regime of the satellite, thus maximizing our ability to collect telemetry.
But why attach the external oscillator then?
One reason to use the external oscillator is for a more stable clock signal. This is especially important for UART communications, but for the SPI and TWI used to communicated with the sensors and radio, it's not so important because a clock signal is provided in those communications. So, for a "ground version" of the AmbaSat that you will need to use UART heavily with, you might want to consider changing fuses (and updating the boot loader) to improve UART reliability.
The other reason for using the 4 MHz resonator is to simply get more work down in the same amount of time. In my opinion, this is not important. Ideally, the AmbaSat is only doing a "collect and report" type function in orbit. All processing of the telemetry really should be done in ground software. This means things like changing sensor reading to human readable floating point values should happen on the ground. However, that's a design choice. A pro-4 MHz argument might be since power will be intermittent given the satellite depending on solar panels and will be tumbling through space, you don't know how long you will have power and so you want to get as much done as possible before the power goes out. I plan to do some experimenting on this at some point to make a more empirical choice. However, if this was your goal, using the internal clock with a smaller divider could =be more power efficient, but still has the UART stability issues.
The fuses I use for using the external 4 MHz resonator are
(E:FE, H:D6, L:F7). Also, I have created a PlatformIO board file for the AmbaSat-1 being configured with these fuses, which you can find here.