@Welch-Jonas Probably you wanted to write 253 instead of 255.
I think you are talking about IPV4 Class C Private networks eg. 192.168.0.x - 192.168.255.x /24 (or netmask 255.255.255.0).
As you know the default IP address of Omega2 WiFi AP is 192.168.3.1, the Network address is 192.168.3.0 and the Broadcast address is 192.168.3.255 - so the usable client IP Range is 192.168.3.2 - 192.168.3.254 ie. 253.
The default DHCP pool of Omega2 is 192.168.3.100 - 192.168.3.249
uci show dhcp
so theoretically max 150 WiFi clients can connect to an Omega2's AP at a time.
BTW I'm afraid OP wants to know how many clients connected to that AP "just know".