I'll time your function, but I don't work weekends
Rebmu: 17 (27 - 10, obfuscated) or 30 unobfuscated

Rebmu is specifically designed to play code golf while being readable (for those who get the "trick"), so the obfuscation rule is against its principle.  But:

DnowRjRkILd/7 6[pDT[adJk]]


It works all day on weekdays:

Input Integer: 10
Input Integer: 20
0:00:00.000008


...but on weekends it just does nothing:

Input Integer: 10
Input Integer: 20


Explanation:

Using the unmushing and noticing capital runs of letters are separate words, and the lack of a leading capital run means we're not making a set-word, we get the abbreviated Rebol:

d: now
r j
r k
il d/7 6 [
    p dt [
        ad j k
    ]
]


Un-abbreviating it, what you wind up with is:

;-- save current date and time into "d"
d: now

;-- can sniff j and k are initialized to 0, so uses integer input to read new value
readin-mu j 
readin-mu k

;-- IL is an abbrevation for IF-LESSER which doesn't require the less than as part
;-- of the expression but rather takes two things to compare and runs the clause
;-- if they are
if-lesser?-mu d/7 6 [
    print delta-time [
        add j k
    ]
]


Date numbers in Rebol are numbered 1 for Monday up to 7 for Sunday.  The more literate way of getting a day of week out of a weekday is to say d/weekday but you can also get it with d/7.  My preferred solution without changing things just to adapt to this problem would be more like:

rJrKilNOW/weekday 6[pDT[adJk]]


But if were to update the vocabulary for general application to this style of problem, which it probably comes up often enough to not want to fall through to verbose Rebol every time, I'd probably make MON thru SUN be 1 - 7) and abbreviate NOW WEEKDAY, at which point it would look probably more like...

rJrKilNW/wkdySAT[pDT[adJk]]


Notes

As usual, you can make "the program" itself a wee bit shorter if you allow the inputs to be passed to Rebmu as arguments and just accept the evaluation result (here, either a value of type time or NONE) without printing it:


  rebmu/args [DnowILd/7 6[dt[adJk]] [J10 K20]


Also delta-time, dates, image generation, and a crazy number of things are already included in Rebol's half-megabyte, zero-install executable.