It depends, jgirl ...
As others have said, only you know your body and how well you've recovered from your marathon .... Just remember that during your weeks of training, and your marathon race day, many, many micro tears in your muscles, tendons and body occurred ... and, although, you may appear to feel fine, physically and mentally, in actuality your body may not necessarily agree deep down ...
And, yes, it is suggested that no hard training for at least 2-3 weeks, though it does not mean no running/training at all .. and, active recovery is recommended ...
How much and how far have you ran since your marathon ???
It is true, that your fitness gains after marathon training, again assuming you came out injury free, remains with you .... and, focusing on the shorter events your 5K and 10K performance may actually be improved considerably ....
We are all different, and have different levels of experience, training and abilities .... For some it may take 4-5 weeks to recover and others, 3-5 days before resuming regular training, it all depends ....
As well, your goals and expectations for the 1/2 Marathon, as noted by others, will have to be outlined before going in .... Plan your race strategy and race your plan ....
In the end, it is your decision .... Take care and all the best in whatever decision you choose ....
