Similar to my recent question about moving between a spell's attacks I am curious about whether RAW you can use a bonus action between a spells attacks.
Unlike in the case of movement, bonus actions do not have a section specifying that they can occur in between parts of a particular type of action. The rules section on bonus actions reads (PHB, 189):
You choose when to take a bonus action during your turn, unless the bonus action’s timing is specified, […]
The answer to this question is very relevant to Warlocks who might use Eldritch Blast against the target of their Hex but slay the target before every blast of Eldritch Blast has been used. The Warlock would then want to target a new creature with the remaining blasts (see this answer on changing targets during a spell) but first use their Bonus Action to move Hex to the new target.
If the particular bonus action is relevant to your answer, you can use the moving of Hex to a new target as the use-case – but I would also appreciate a general understanding of when, if ever, bonus actions can split up a spell's attack.
Related: Can you use a bonus action from Cunning Action in the middle of an Attack action?
Best Answer
Yes, you can use a bonus action at any time (including in the middle of an action) unless specified otherwise
As you quoted in the question itself, the rules on bonus actions state (emphasis mine):
In essence, you can take a bonus action at any time on your turn if its timing is not specified. Unless your ability to take the bonus action is dependent on a particular action being completed, nothing prevents it from happening in the middle of the multiple attacks of a spell.
The hex spell, for instance, states:
Say you've cast hex on a target on a previous turn, and you're level 5, so your eldritch blast spell creates 2 beams. If you cast eldritch blast and your first beam reduces the target to 0 HP, you can use a bonus action to move your hex to another target before you make the attack for your second beam.
Rules designer Jeremy Crawford reiterated this fact in an unofficial tweet from May 2018 (after some people were confused by an earlier tweet meant to indicate that bonus actions dependent on the Attack action could not occur between the multiple attacks of that action):
The clarification repeats what the rules indicate: bonus actions whose timing is not contingent on a specified action can be taken at any time, including in the middle of an action.