Looking on the internet deeply has found these results:

slot available is the most popular phrase on the web.

slot open 1478,000 results on the web	slot available 1785,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
He's hypertensive, and the OR had a slot open, so I rushed over here. That's how much I care about my patient. I'll keep a slot open, just in case. no No There was an exam slot open, but only one. There's an analyst slot open in Caribbean Affairs at... It's downtown, but there's a slot open in the fall. And right now, there's one slot open.	You know I only have one slot available in my entertainment center. F also offers great freedom when it comes to the choice of operating system drive type and placement, with M. slot available. I may have a slot available 6:30 a.m. Saturday mornings. E8 Excellent, let's see when we've got a slot available... The server also carries an asset tag for fast identification. RS400 PS2 It is an issue that needs our discussion and therefore my group wishes to propose to this House that we use the third slot available on Thursday afternoon for consideration of the issue of Taiwan's participation in the World Health Organisation.

slot open

1478,000 results on the web

slot available

1785,000 results on the web

More popular!

He's hypertensive, and the OR had a slot open, so I rushed over here. That's how much I care about my patient.
I'll keep a slot open, just in case.
no
No
There was an exam slot open, but only one.
There's an analyst slot open in Caribbean Affairs at...
It's downtown, but there's a slot open in the fall.
And right now, there's one slot open.

You know I only have one slot available in my entertainment center.
F also offers great freedom when it comes to the choice of operating system drive type and placement, with M. slot available.
I may have a slot available 6:30 a.m. Saturday mornings.
E8
Excellent, let's see when we've got a slot available...
The server also carries an asset tag for fast identification. RS400
PS2
It is an issue that needs our discussion and therefore my group wishes to propose to this House that we use the third slot available on Thursday afternoon for consideration of the issue of Taiwan's participation in the World Health Organisation.