What is the deadline for collecting required number of signatures?

UK Public General Acts, Recall of MPs Act 2015, accessed 26 January 2021

7. Where and from when the recall petition may be signed

(1) Where the petition officer for a constituency receives a Speaker's notice, the officer must, as soon as reasonably practicable, designate—

(a) a place, or places, at which a recall petition is to be made available for signing, and

(b) a day from which the petition is to be made available for signing. […]

(4) The petition officer must designate under subsection (1)(b)—
(a) the day which is the 10th working day after the day on which the officer received the Speaker's notice, or
(b) if it is not reasonably practicable to designate that day, the first subsequent working day that it is reasonably practicable to designate. [...]

9. Recall petition to be made available for signing

(1) The petition officer must ensure that the recall petition is made available for signing throughout the signing period at the designated place or places, and by post, in accordance with regulations under section 18.

(2) In this Act “the signing period” means the period of 6 weeks beginning with the designated day. […]

6 weeks beginning with the designated day