The ML1K is Allen Bradley's bottom dweller. Unlike other AB PLCs which have user configurable data tables, all of the data tables of this PLC are fixed in size. Each timer occupies 3 16 bit words in memory. This is the timer data size, not counting the memory occupied by the program which holds the timer instruction itself.
In a PLC when you see that it has 1K of memory, that is 1K words of memory, or 2048 bytes. In addition to 40 timers, the ML1K also has 32 words of bit files, 32 counters (3 words each), 16 instruciton control elements, 3 words each, and 105 integers, and 15 program files, leaving about 600 words for the user program - which is quite a bit as PLC programs are relatively compact.