頭先=just a short while ago;a moment ago;just now, e.g:頭先妳条仔打電話俾妳（Your boyfriend called you just a moment ago.） *maybe more than 5 minutes 啱啱=only just.just now e.g:你點解唔嚟早一步，姖啱啱走咗！(why didn't you come earlier, she only just leave.) *maybe less than 5 minutes =only; just 恰恰好 e.g: 呢隻火雞啲火候啱啱好。 the duration of the turkey is just ok. e.g: 啱啱够時間赶上班機。Just made the plane./We're just in time to catch the plane. just my opinion, actually, in our daily life, we are not very clear to distinguish the differece between them.

Actually, there is no different for me, but i think 啱啱 is much politer

i think they are the same,just like 刚刚 刚才in Chinese ...i think^^

for me, it is no different. both also can use.