A timestamp is in fact a type P(8) number which holds year, month, day, hour, minute and second. There is an actual type TIMESTAMP available and there is a statement to populate your timestamp with "now". But there's more..
The statement to populate your timestamp variabele with the current date and time is
DATA: lv_timestamp type timestamp. GET TIME STAMP FIELD lv_timestamp.
Feed your timestamp to the WRITE statement and you'll get something like
20.150.619.151.126
Easy formatting can be done with
write: / lv_timestamp using EDIT MASK '____/__/__ __:__:__'. 2015/06/19 15:11:26
If you need some calculating on timestamp data, there is a class CL_ABAP_TSTMP that may be useful. Here's an example that gets the current timestamp and subtracts a number of hours (5) from it:
DATA:
lv_timestamp type timestamp,
lv_seconds TYPE p.
GET TIME STAMP FIELD lv_timestamp.
write: / lv_timestamp.
lv_seconds = 5 * 60 * 60.
lv_timestamp = cl_abap_tstmp=>SUBTRACTSECS( exporting
TSTMP = lv_timestamp
SECS = lv_seconds ).
write: / lv_timestamp.