Gus Rentfro had a web page that talked about feeding boas.
bcr touched on very good points about feeding a young boa.
I will just add that ALL signs of any previous meal should be gone. Gus mentioned that your boa should have completely eliminated all waste before feeding again.
There is also scientific/biological evidence that shows the enlargement of the organs and a mass transfer of energy in a boa that is digesting a meal. The process should fully complete before feeding again in order to let the system reset.
There is more to the process and a great deal of variability. Wild boas will often feast and famine. It is their design by nature. If you do some back to back feeding you will not necessarily harm your boa, but you have to make it up on the other end.
Seasonality is important. Adult boas do not eat year round and really shouldn't.
Now a younger snake being fed small meals weekly will get a good start and grow quickly.
My advice is to read THE COMPLETE BOA CONSTRICTOR by Vincent Russo. There is excellent feeding advice in the book and also a good explanation of the "seasonality" (seasonal changes that the animal follows) that is worth reading.
In a nutshell, feed conservatively.
In nature the largest boas are the oldest boas. Your snake will grow healthy and live long if you don't over feed.