I think "Quedar" - is more permanent staying, e.g: I will stay in this country until I die, Me voy a quedar en ese pais hasta que morir
"Estar" - is being someplace, or in some sort of state. e.g: are you well? Estas bien? where are you ? donde estas?
forum talk about the same subject as reference: http://forum.wordreference.com/showthread.php?t=377928 It's very interesting ") Hope this helps!
"Very late" would be "muy tarde." "Más" means "more"... but with English comparative statements, "more late" becomes more properly "later." (Note: If "later" had more syllables, we'd keep the word "more"--consider how we say "more beautiful" rather than "beautifuler.") Hope that helps. :)
Regarding the "how late" - it is actually quite literal compared to English:
☆ Tarde || Late
• Más || More
• Mucho || Much
... LateR = more late || Más tarde
... Much later = much more late || Mucho más tarde
• Muy || Very
... Very late || Muy tarde
... More than "very" late = very very late || Muy muy tarde
[Note] Tarde, más tarde, etc. (adverb) point to being delayed. "Luego" as "later" means: then; afterwards; soon; next time.
SpanishDict does translate "I'm going to be here later on" as "Voy a estar aquí más tarde" but leaves off the word "on" in the reverse translation, possibly since the adverb is superfluous; the English sentence means essentially the same with or without the "on." (Perhaps for that reason, "later on" sounds more casual to me than simply "later.") If you feel "later on" is a more natural way to say the English sentence, then the next time you get this question, report to DL that your translation should be accepted.
• Luego as "later" means then, afterwards; soon; next time
• Tarde as an [adverb] means "late" (and más tarde = later) as in being delayed - being late from somewhere, staying somewhere late/-r, etc.
... Tarde as a [noun] means the afternoon/ early evening (after noon/lunch - before sundown).