Rent your darkroom by the hour or session and let members book and pay online. Booker shows live availability on your product page and stops two people booking the same bench.
How it works
Set a unit length and let people book the time they need for developing and printing.
Offer each darkroom or bench as its own bookable space with its own rate (Pro plan).
Held at add to cart, blocked at checkout, so no two members book the same slot.

Every session on one admin calendar, with optional Google Calendar sync on the Starter and Pro plans.

Questions
Yes, on the Pro plan. Set each up as a separate space, or use pricing tiers if they share a calendar at different rates.
They can book any available slot whenever they need one. Each booking blocks that time for everyone else.
Through your Shopify checkout, so you keep your existing payment setup.