A Consideration on Timing
In the programs that I lead, I prefer to have a span of at least 1 week between prompts. This period allows enough time that the prompt falls into the background, arising occasionally, and allows the subconscious to work at it. This often brings up unexpected memories and creative connections between items you might encounter and the responses you came to. It gives opportunity for chance discoveries.
There is no time limit on the response or on the item selection. You can be responding to a prompt and adding items relating to it for as long you like. But I feel it is best to not rush the process. Focusing on just one prompt at a time, at least in the first pass through the prompts, helps go deeper into the prompt and what it can offer.