Torque uses strings fairly often, possibly for everything. Add one to a string that starts with a number followed by non-numeric characters, and it ignores everything but the number. Schedule probably demands an integer only, so probably only reads up to the first non-number, even though the rest would be a valid number for a floating point type. So, it probably takes the first 1.8, discarding the rest, and occurs almost instantly.
Test results:
1e8: instant
1e7: instant
1e6: instant
1e5: delayed
1e4: delayed
10000000000000000000: delayed
10000000000000000000+1: instant
...
1000000+1: instant
100000+1: delayed
999999+1:instant
999998+1:delayed
1000000-1:delayed
Conclusion: Schedule can accept arbitrarily long integer constants, but numbers at or above one million that are the results of any sort of math will not work.
Also, storing a very long number in a variable and then using it has no problem, as long as no math is involved. Untested: passed as a function argument, returned from a function.
Also: string functions do not cause long numbers to become short.
So, my conclusion: schedule will not accept a floating point number at or above one million, but will accept a string or unaltered number above one million.
Edit: numbers at or above one million with a decimal will become instantaneous, too.