seedling stage can be pretty long and it's different for everyone, all depending on your growing medium, strain, methods and environment. These things can't be rushed and there's no set time for when you need to start nutes; my plants let me know when they were ready by showing me deficiencies. there's a tonne of guides on these forums that cover all growing media and conditions, you can follow these but allow some leeway for your strain which may respond more slowly or more quickly than those in the guide. make sure you find a guide that covers the media you grow in, such as coir (what i use) as these can vary drastically and have disparate
guidelines.
the seedling stage is well known to be the period in which patience is a boon; history is full of growers who started nutes too early to try and speed things up in this stage; many of them failed. in this game, google is your best friend and this site is your second best friend because what you can't figure out on google can be posited here in the form of a question and we'll answer if we can.
don't get tempted to try to artificially speed things up as you could murder them. I felt the same when my plants were very small; my particular strain sprouted from dry seed in less than 2 days and got to about an inch and then sat there for a week, then grew more, then went back into chillin snail mode.. it ebbed and flowed like that until .. it's still happening.
the first grow is definitely the hardest, there have been times when I've thought about throwing the head up and dumping the lot but I'm glad i didn't, I've learned loads and i know I've so much more to learn before i can call myself a proper grower. you just have to be persistent. if you fail, start again, and keep going until something stops you (money, cops etc)
and if you have questions and can't find the answers, ask. like i said, someone will answer if we can.
keep the faith brother.