The command "lease 0 12" set the duration of the lease (the time during which a client computer can use an assigned IP address). The syntax is "lease {days[hours] [minutes] | infinite}". In this case the lease is (0 day) 12 hours.
We also notice that the pool of IP addresses that can issue to the clients are rather small as the network 192.168.1.0/24 only supports 253 assignable IP addresses. But the first 49 IP addresses were excluded so we only have 253 - 49 = 204 assignable IP addresses < 300 users.
Therefore the best solution is here to reduce the time of each issued IP address (to 2 hours instead of 12 hours) as they only need to use in 2 hours per day, thus increasing the chance of reuse the IP addresses for the clients.