I am actually more interested in far OOM options like 0,10 or 0,05 delta. Thanks anyway
If you're dealing with those kind of wings, its probably best to eschew explicitly calcing the theta decay (unless you're capturing the daily steepening of the skew) - you'll probably finding your model telling you it quickly becomes worthless, while in reality it'll keep a bid. I'd say to just look at the current weeklies that have the same time to maturity that you're interested in. Ie, if you're selling the 1m 5d put, and want to know its value in 1 week, look at where the 3 week 5d put is pricing. As with everything, its imperfect, but probably the simplest, most robust means.