$ ls
data
$
$
$
$
$
$ cat data
100 ABC A123
100 BVC D234
100 BNC N324
200 CBC A122
200 AVC D294
200 HNC N324
300 GBC A173
300 FVC D234
300 DNC N344
$ awk -v timestamp=whatever  '{print $0 >> ($1timestamp".txt")}'  data
$ ls
100whatever.txt 200whatever.txt 300whatever.txt data
$ cat 100whatever.txt
100 ABC A123
100 BVC D234
100 BNC N324
$