Tried the S5T11H_12M_18S but it will not accept that
Bold part is your problem.
To understand this, you need to know how the S5 time is built.
S5 time is only 1 word, 2 byte, 16 bits.
Of those 16 bits, the 2 MSB's are not used. This being bit 14 and 15.
Bit 12 and 13 together form a binary number which makes the time base.
00 = time base is 10ms
01 = time base is 100ms
10 = time base is 1s
11 = time base is 10s
The following 12 bits is expected as a BCD number.
It looks something like:
NNTT XXXX XXXX XXXX
N = not used
T = time base
XXXX = BCD number (0-9 in hex)
The BCD x Time base = S5 time.
This setup limits the timer to 9990s. (BCD 999 and time base of 10s)
As uptown said, this effectively limits the timer to 2h46m.
As some other will no doubt mention: Seeing that you're just starting with Siemens, make it a habit to use IEC timers now.