Delay pppoa network connection creation

Basically title. I've a costum build for my TD-W8970, but this happens also on last stable official OpenWrt build.

My router is trying too hard to bring up the wan interface. The whole process takes just few seconds but the log is swarmed by failed attempts:

<.... date ... > daemon.notice netifd: Interface 'wan' is setting up now
<.... date ... > daemon.err insmod: module is already loaded - slhc
<.... date ... > daemon.err insmod: module is already loaded - ppp_generic
<.... date ... > daemon.err insmod: module is already loaded - pppoatm
<.... date ... > daemon.info pppd[ ... ]: Plugin pppoatm.so loaded.
<.... date ... > daemon.info pppd[ ... ]: PPPoATM plugin_init
<.... date ... > daemon.info pppd[ ... ]: PPPoATM setdevname_pppoatm - SUCCESS:0.8.35
<.... date ... > daemon.notice pppd[ ... ]: pppd 2.4.7 started by root, uid 0
<.... date ... > daemon.err pppd[ ... ]: connect(0.8.35): No such device
<.... date ... > daemon.info pppd[ ... ]: Exit.
<.... date ... > daemon.notice netifd: Interface 'wan' is now down

An this goes on on a loop for at least 30 seconds until this came up:

<.... date ... > daemon.notice dsl-notify: Switching to TC-Layer ATM
<.... date ... > kern.info kernel: [ ... ] ATM1.0.26    ATM (A1) firmware version 0.24
<.... date ... > kern.warn kernel: [ ... ] ifxmips_atm: ATM init succeed

After that another 2 attempts are made. The first seems to work but it fails asap like this

< ... date ... > daemon.notice pppd[ ... ]: pppd 2.4.7 started by root, uid 0
< ... date ... > kern.info kernel: [ ... ] pppoa-wan: renamed from ppp0
< ... date ... > daemon.info pppd[ ... ]: Using interface pppoa-wan
< ... date ... > daemon.notice pppd[ ... ]: Connect: pppoa-wan <--> 0.8.35
< ... date ... > daemon.info pppd[ ... ]: LCP terminated by peer
< ... date ... > daemon.notice pppd[ ... ]: Connection terminated.
< ... date ... > daemon.notice pppd[ ... ]: Modem hangup

And the last one succeed:

< ... date ... > daemon.info pppd[ ... ]: CHAP authentication succeeded
< ... date ... > daemon.notice pppd[ ... ]: CHAP authentication succeeded
< ... date ... > daemon.notice pppd[ ... ]: local  IP address < ... >
< ... date ... > daemon.notice pppd[ ... ]: remote IP address < ... >
< ... date ... > daemon.notice pppd[ ... ]: primary   DNS address < ... >
< ... date ... > daemon.notice pppd[ ... ]: secondary DNS address < ... >
< ... date ... > daemon.notice netifd: Network device 'pppoa-wan' link is up

On previous build (LEDE 17.06) this wouldn't happend (only the last two attempts were made).

Is there a way to tell OpenWrt to just wait 30 seconds before trying to connect to wan? Or to do it after the whole " Switching to TC-Layer ATM".