Can you put a comma after when

Use a comma after introductory adverbs.

Adverbs that don't end in "ly," such as "when" or "while," usually introduce a dependent clause, which rule number two in this post already covered. Also insert a comma when "however" starts a sentence, too.

Use Commas to Separate Items in a List. This probably the first use of commas you learned in school: separating items in a list of three or more things. Here's an example: The cake mix requires flour, sugar, eggs, and butter. Note that some style guides would not add the comma after the word "eggs".