Oh sure you can play with the timings without hurting anything. The worst that will happen is it won't boot, and you will have to either clear CMOS on the MB or do it from BIOS to get it back to OEM. (I don't know ASRock's BIOS so I can't tell you which.
You can find out what the SPD timings chart is for your RAM from CPUZ
, if you don't already have it.