I would part a hard date on there, as it shows a commitment to actually getting out as opposed to "seeing what's out there". They're not going to want to set up for a start date only to have you sent TDY somewhere and your departure date pushed back.

My command reneged on my terminal leave and sent me TAD for 1/2 of it, but I had not advertised being available before then. You can usually start early if it works out...but to be honest, the terminal leave is nice as it's proving to not be as easy as anticipated to leave (way much paperwork).

My $.02
Spongebob