Quoting baking my bun:" I'm not timing but I can tell they are totally irregular - I was just wondering if they can be one sided? ... [snip!] ... they are contractions it is veerrrryyy early so not going to go calling anyone just yet, lol. Plus I want my own bed tonight!"
It can be, or just be braxton hicks.
Definitely go to sleep, just in case it is the real thing you need to sleep while you can actually sleep through them. I didn't and I regretted it after four days of labour and no sleep!
Mine started off really irregular, maybe every half hour to an hour, then they slowly got closer together and more intense/longer.