Hey since it's a 'low on time' thing I'll give some suggestions on trying to maximize that time.

Herb/alch can work - but a lot of the time alchemy isnt profitable (this is highly server dependant) - and unless you have the time to babysit auctions this could be an unreliable source of income.

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What I would suggest considering is maybe look at the idea to switch from Herb/Alch to Herb/mining. As you're flying around to M+, or raids or whatever - pick up everything you find along the way...this stuff usually sells quickly and consistently and you don't need to worry about profit margins and stuff. Look up some routes (gathermates/routes addons), and travel along the hotspots on your way to/from places. You can glide around while in queue, or waiting for people as well.

The same can be done with fishing, you can do that almost anytime. For example when you're queueing up for an island expedition or something, you can fish right there off the dock for a little bit.

Just some ways that you can think about getting the most out of your limited time.