Hi Diana,
yes you can try to stretch this timing a little, especially during the winter/spring months when there are less mould spores present in the air. We’ve certainly had good success doing 2 day collections at these times of the year.
However, you are likely to find increased contamination rates when doing this in the summer in particular, when there are more mould spores in the air and warmer temperatures (this means the mould spores will already be growing on coffee by the time you inoculate). If the cafe can keep the grounds in a fridge/cold room for you this would help, or it may be worth looking to collect from larger cafes if there are any near to you. Also if the grounds are collected in a sealed container this also helps to keep them clean.
Hope this helps and your first bags are starting to grow well?
Adam