While selecting resistors most often if standard values aren't present , the closest standard values are used which might be a kilo ohm or two away from the design requirements . I want to know how much leeway is there while choosing an inductor or capacitor .I couldn't find a 0.6nH for L1 in the below interfacing circuit and the ones I have ordered are about a week or two away from being delivered and I was sort of wondering if I could use another ballpark value (say 9.9nH) in its place. L1 in combination with C2 is used as some sort of LPF I think to remove ripples from supply voltage to the low noise amplifier SKY65404.
There's no general answer to your question. There are lots of factors to consider when selecting an inductor (e.g. ESR, saturation current, interwinding capacitance, lossiness including core and AC losses, etc.).
I wouldn't consider 9.9nH to be "in the ballpark" of 0.6nH as it's more than a decade higher in inductance. In this case, it seems like more inductance would be better at filtering the power supply, but if there are supply transients drawn by the part the higher inductance could lead to higher ringing and overshoot so it would be best to go with the inductance specified in the datasheet.
I'm surprised that they don't give more information about acceptable inductors in the datasheet, because the type of inductor can have a big impact on performance. I would expect that a lossy inductor (maybe a ferrite bead) would be preferred in this application, but again no guidance in the datasheet. I would check to see what they use on the evaluation board for the part and go with that since you know that it has been tested.
When selecting alternate values for a component, think about the relative change in value, rather than the absolute change.
If the design calls for a 20K resistor, using 18K or 22K will probably be fine, as that is only a 10% change.
If the design calls for a 5K resistor, using 3K or 7K instead will probably not work - this is the same 2K off the desired value, but is now 40% "wrong".