I went to seetook a peek at Lang-8 this morning because its last day is coming up. I took a peek at Lang-8 this morning because its last day is coming up.

This is to more closely resemble your original Japanese text.

I went to seecheck up on Lang-8 this morning because its last day is coming up. I went to check up on Lang-8 this morning because its last day is coming up.

I went to seecheck Lang-8 this morning because its last day is coming up. I went to check Lang-8 this morning because its last day is coming up.

Actually, it'Come to think of it, its last day is already tomorrow! Come to think of it, its last day is already tomorrow!

"Come to think of it" was to more closely match your Japanese. "It's already tomorrow" is also fine, but might be a little confusing, so I made it more explicit.

ActuallyIn fact, it's already tomorrow! In fact, it's already tomorrow!

AIt's actually, it's already tomorrow! It's actually already tomorrow!

Earlier, I was informed by a user that there is/was someone preparing a successor site. Earlier, I was informed by a user that there is/was someone preparing a successor site.

Technically the verb within the subordinate clause should match the main verb. Here, the main verb is "informed," so we can change "is" to "was." But, keeping it as "is" is also okay.

Earlier, I was informed by a user that there is someone pcreparating a successor site. Earlier, I was informed by a user that there is someone creating a successor site.

Earlier, I was informed by a user that there is someone preparing a successor site.

Earlier, another user told me that someone is making a similar site.

And today I tried the application to transfer/migrate past posts (from Lang-8 to the new site), which was provided by the user. And today I tried the application to transfer/migrate past posts (from Lang-8 to the new site), which was provided by the user.

And today, I tried using the application to transfer past posts, which was provided by the userprovided by the user to transfer previous posts. And today, I tried using the application provided by the user to transfer previous posts.

Previous post from lang-8?

And today I tried the application to transferplug-in to export past posts, which was provided by the usernew site. And today I tried the plug-in to export past posts, which was provided by the new site.

But I gave up on it because it seemedwas going to take too needmany hours on my slow Chromebook. But I gave up on it because it was going to take too many hours on my slow Chromebook.

This sounds more natural.

But I gave up on it because it seemed to needtake hours on my slow Chromebook. But I gave up on it because it seemed to take hours on my slow Chromebook.

But I gave up on it because it seemed to needtakes so many hours on my slow Chromebook. But I gave up on it because it takes so many hours on my slow Chromebook.

OR: ... it takes to much time on my slow Chromebook.

But I gave up on it because it seemed to need hours on my slow Chromebook.

But I gave up on it because my slow Chromebook would take hours.

IBut it's okay because I've taken all the needed notesransferred all the notes I needed to my Blogger blogaccount. But it's okay because I've transferred all the notes I needed to my Blogger account.

It's okay because I've taken all the needed notes to my Blogger blog.

It's okay because I've already taken all the notes I needed to my Blogger.

I am going to try the new site, Nyan-8, when it has startedlaunches. I am going to try the new site Nyan-8 when it launches.

I am going to try the new site, Nyan-8, when it has startedlaunches. I am going to try the new site, Nyan-8, when it launches.