60 lbs in a 55 is fine, but don't go stirring it up with power heads and cleanings... it will be a nice base for denitrifying bacteria long term.
The only way to know when the tank will be ready will be to watch it cycle. Once you mix the rock, watch for growth on the dry rock, when it happens you won't be able to miss it. You can't put a time frame on something like that because there are so many factors involved. From water quality to light, to rock quality, sand quality, and whatever organisms come in on the live rock and in the live sand. Every tank is an individual, and this is a good time to understand that from this point on, it tells you... no more of you tell it anything. This is a living environment and it needs time to grow and mature, and it will do it at its own rate. You can't speed it up, only slow it down by being impatient. If you rush things, bad things tend to happen, and then the wait for the great thing you envisioned gets to be that much longer in the future. If you are patient, take your time and do it right, good things come of it in the end.
After your tank has cycled, start watching for the bare rock to start growing things like coraline algae, sometimes small polyps or other invert life... worms and such will begin to appear from within the rock and on the rock. That is a good indication it is curing and the tank is ready for it's first animal. Add animals slowly so as not to overwhelm newly cured rock with a waste load it can't yet handle. 1 fish at a time... keep it low and under control.
And, most important, watch calcium and carbonate hardness levels during the entire process. This is something many people forget about, and if those levels are off, it will affect the way your rock cures and the animals that will go into the tank. This is something that will fluctuate over time, so should be monitored regularly. Some of those rocks may leech calcium into your water, from breakdown and debris, and that will need water changes and such to fix it.
I always start my new tanks with the clean up crew first unless its a fish only system. When you get to that phase we can talk you through it.
For now, be patient.... over anything else, if you want this to go smoothly and easy. Life takes time.