When can I spend downtime?

I have a character that I haven't played in a while, who has been working towards proficiency in the Herbalism Kit; he's got 107 days spent towards it. I have recently found out about the new Factions Guide which says that Emerald Enclave members can learn (among others) Herbalism Kit proficiency with 125 downtime days spent. So, can I make an entry now that he spent the extra days and lifestyle to learn it, or do I need to wait until he is in another mod?

You should just be able to make an entry in the Notes section of your last adventure, spend the DTD and Lifestyle gold, and be good to go

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