the terminology you are looking for in general is the word "cooldown", in the case of hero respawning the term in "revive time".
the amount of time it takes for heroes to revive is based on a complex formula, the numbers of which can all be found in advanced -> gameplay constants, under the "Hero XP Gained" fields. The 4 fields to look out for are Constant Factor, Level Factor, Previous Value Factor and Table.
Experience Tables 101
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The overall purpose of these four fields is to define a value of experience for every possible level. The "Table" field does this by simply specifying exactly that, an experience value for each level.
For example:
Hero XP Gained - Hero, Table = 100,120,160,220,300
which means that a hero will receive 100 XP for killing a level 1 hero, 120 XP for killing a level 2 hero, and so forth.
Now then, explicitly setting a value for every single hero level can be tedious and wasteful if you have a lot of hero levels (say, 500). So, the three formula fields are used to calculate all values beyond those in the existing table field.
This formula computes the experience value "f(x)", for level "x", based on the level and previous experience value, as well as a constant:
f(x) = C + L*x + P*f(x-1)
where
C = Constant Factor field
L = Level Factor field
P = Previous Value field
Continuing our example using the Hero XP Gained - Hero fields (C = 100, L = 0, P = 1), the experience gained from killing a level 6 hero would be:
100 + 0*6 + 1*300 = 400
Note that the 300 is the experience for level 5, which comes from the table. For level 7, we get:
100 + 0*7 + 1*400 = 500
and so on. This particular equation is quite simple, it just adds 100 more for every level.
Now we can look at the Hero XP Gained - Normal fields, where
Table = 25 (only one entry!)
C = 5
L = 5
P = 1
and compute
f(1) = 25 (from table)
f(2) = 5 + 5*2 + 1*25 = 40
f(3) = 5 + 5*3 + 1*40 = 60
f(4) = 5 + 5*4 + 1*60 = 85
f(5) = 5 + 5*5 + 1*85 = 115
and so on.
