How much lme do you have? What style beer? You can do all at 60 mins, but better to do half at 60 and the other half at 15 mins, as this won't male the beer darker.
I generally add half at the start and half at the end. You want to boil some of it the entire time, but boiling all of it can contribute some flavors you don't want. This can also help keep your beer's color lighter, if that's something you care about.
Some people also claim it helps hop utilization, but others have found no evidence for this.
Half at the beginning or less mixed with the steeped grain wort will do. The other half at flame out,cover & steep 15 minutes will pasteurize it. I took it a step further & use half a 3lb bag of plain DME in the boil for hop additions. Then the remaining DME & all the LME at flame out. Color is even lighter,& flavors are def better.
I put it in after "flame out". Otherwise, my stove top has a hard time returning to boil if I stir the LME in without keeping the heat on and possibly burning the LME. I once poured 15.3lbs of LME while cooling a batch of RIS in my sink.
I do half at start and half at 15 minutes to go for lighter colored beers. For stouts and such I do it all at the beginning as the extra carmelization should have little effect.